Geometry. Points, Lines, Planes & Angles. Part 2. Angles. Slide 1 / 185 Slide 2 / 185. Slide 4 / 185. Slide 3 / 185. Slide 5 / 185.

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1 Slide 1 / 185 Slide 2 / 185 eometry Points, ines, Planes & ngles Part Part 1 Introduction to eometry Slide 3 / 185 Table of ontents Points and ines Planes ongruence, istance and ength onstructions and oci Part 2 ngles ongruent ngles ngles & ngle ddition Postulate Protractors Special ngle Pairs Proofs Special ngles ngle isectors ocus & ngle onstructions ngle isectors & onstructions Slide 5 / 185 ngles click on the topic to go to that section Slide 4 / 185 Table of ontents for Videos emonstrating onstructions ongruent ngles ngle isectors Slide 6 / 185 ngles click on the topic to go to that video efinition 8: plane angle is the inclination to one another of two lines in a plane which meet one another and do not lie in a straight line. Whenever lines, rays or segments in a plane intersect, they do so at an angle. Return to Table of ontents x

2 Slide 7 / 185 ngles The measure of angle is the amount that one line, one ray or segment would need to rotate in order to overlap the other. Slide 8 / 185 ngles In this course, angles will be measured with degrees, which have the symbol 0. In this case, Ray would have to rotate through an angle of x in order to overlap Ray. or a ray to rotate all the way around from, as shown, back to would represent a angle. x x Slide 9 / 185 Measuring angles in degrees Slide 10 / 185 Measuring angles in degrees The use of 360 degrees to represent a full rotation back to the original position is arbitrary. The use of 360 for a full rotation is thought that it come from ancient abylonia, which used a number system based on 60. ny number could have been used, but 360 degrees for a full rotation has become a standard Their number system may also be linked to the fact that there are 365 days in a year, which is pretty close to is a much easier number to work with than 365 since it is divided evenly by many numbers. These include 2, 3, 4, 5, 6, 8, 9, 10 and 12. Slide 11 / 185 Right ngles Slide 12 / 185 Right ngles efinition 10: When a straight line standing on a straight line makes the adjacent angles equal to one another, each of the equal angles is right, and the straight line standing on the other is called a perpendicular to that on which it stands. The only way that two lines can intersect as shown and form adjacent equal angles, such as shown here where ngle = ngle, is if there are right angles, x x ourth Postulate: That all right angles are equal to one another. ot only are adjacent right angles equal to each other as shown below, all right angles are equal, even if they are not adjacent, for instance, all three of the below right angles are equal to one another. x x 90 0

3 Slide 13 / 185 Right ngles This definition is unchanged today and should be familiar to you. Perpendicular lines, segments or rays form right angles. Slide 14 / 185 Right ngles There is a special indicator of a right angle. If lines intersect to form adjacent equal angles, then they are perpendicular and the measure of those angles is It is shown in red in this case to make it easy to recognize When perpendicular lines meet, they form equal adjacent angles and their measure is Slide 15 / 185 Obtuse ngles efinition 11: n obtuse angle is an angle greater than a right angle. Slide 16 / 185 cute ngles efinition 12: n acute angle is an angle less than a right angle Slide 17 / 185 Straight ngle definition that we need that was not used in The lements is that of a "straight angle." That is the angle of a straight line. Slide 17 (nswer) / 185 Straight ngle definition that we need that was not used in The lements is that of a "straight angle." That is the angle of a straight line. nswer This is a type of obtuse angle questions to discuss with a partner: Is this an acute or obtuse angle? What is the degree measurement of the angle? 2 questions to discuss with a partner: Is this an acute or obtuse angle? What is the degree measurement of the angle?

4 Slide 18 / 185 Reflex ngle Slide 19 / 185 ngles nother modern definition that was not used in The lements is that of a "reflex angle." That is an angle that is greater than In the next few slides we'll use our responders to review the names of angles by showing angles from 0 0 to in 45 0 increments. ngles can be of any size, not just increments of 45 0, but this is just to give an idea for what a full rotation looks like. This is also a type of obtuse angle. Slide 20 / This is an example of a (an) angle. hoose all that apply. acute Slide 20 (nswer) / This is an example of a (an) angle. hoose all that apply. acute obtuse right 0 0 obtuse right nswer 0 0 reflex reflex straight straight Slide 21 / This is an example of a (an) angle. hoose all that apply. Slide 21 (nswer) / This is an example of a (an) angle. hoose all that apply. acute obtuse acute obtuse nswer right reflex 45 0 right reflex 45 0 straight straight

5 Slide 22 / This is an example of a (an) angle. hoose all that apply. Slide 22 (nswer) / This is an example of a (an) angle. hoose all that apply. acute acute obtuse right obtuse right nswer reflex 90 0 reflex 90 0 straight straight Slide 23 / 185 Slide 23 (nswer) / This is an example of a (an) angle. hoose all that apply. 4 This is an example of a (an) angle. hoose all that apply. acute acute obtuse right obtuse right nswer reflex reflex straight straight Slide 24 / 185 Slide 24 (nswer) / This is an example of a (an) angle. hoose all that apply. 5 This is an example of a (an) angle. hoose all that apply. acute acute obtuse right reflex obtuse right reflex nswer and straight straight

6 Slide 25 / This is an example of a (an) angle. hoose all that apply. Slide 25 (nswer) / This is an example of a (an) angle. hoose all that apply. acute acute obtuse right reflex straight obtuse right reflex straight nswer and Slide 26 / This is an example of a (an) angle. hoose all that apply. Slide 26 (nswer) / This is an example of a (an) angle. hoose all that apply. acute acute obtuse right obtuse right nswer and reflex reflex straight straight Slide 27 / This is an example of a (an) angle. hoose all that apply. Slide 27 (nswer) / This is an example of a (an) angle. hoose all that apply. acute acute obtuse right reflex straight obtuse right reflex straight nswer and

7 Slide 28 / This is an example of a (an) angle. hoose all that apply. Slide 28 (nswer) / This is an example of a (an) angle. hoose all that apply. acute acute obtuse right reflex obtuse right reflex nswer and straight straight Slide 29 / 185 Slide 30 / 185 aming ngles Interior of ngles n angle has three parts, it has two sides and one vertex, where the sides meet. ny angle with a measure of less than has an interior and exterior, as shown below. In this example, the sides are the rays and and the vertex is. side vertex x side xterior x Interior Slide 31 / 185 aming ngles Slide 32 / 185 aming ngles n angle can be named in three different ways: The angle shown can be called,, or. y its vertex ( in the below example) y a point on one leg, its vertex and a point on the other leg (either or in the below example) leg x vertex leg Or by a letter or number placed inside the angle (x in the below) When there is no chance of confusion, the angle may also be identified by its vertex. The sides of are rays and 32 The measure of is 32 degrees, which can be rewritten as m = 32 o.

8 Slide 33 / 185 aming ngles Slide 33 (nswer) / 185 aming ngles Using the vertex to name an angle doesn't work in some cases. Why would it it would be unclear to use the vertex to name the angle in the image below? ow many angles do you count in the image? y x Using the vertex to name an angle doesn't work in some cases. Why would it it would be unclear to use the vertex to name the angle in the image below? nswer ow many angles do you count in the image? there is more than 1 angle with as its vertex. There are 3 angles y x Slide 34 / 185 aming ngles Slide 34 (nswer) / 185 aming ngles What other ways could you name, and in the case below? (using the side - vertex - side method) nswer What other ways could you name, and in the case below? (using the side - vertex - side method), and x, y, x+y y x y x ow could you name those 3 angles using the letters placed inside the angles? Slide 35 / 185 Intersecting ines orm ngles When an angle is formed by either two rays or segments with a shared vertex, one included angle is formed. Shown as x in the below diagram to the left. When two lines intersect, 4 angles are formed, they are numbered in the diagram below to the right. ow could you name those 3 angles using the letters placed inside the angles? Slide 36 / 185 Intersecting ines orm ngles These numbers used have no special significance, but just show the 4 angles. When rays or segments intersect but do not have a common vertex, they also create 4 angles. x x

9 Slide 37 / Two lines meet at more than one point. Slide 37 (nswer) / Two lines meet at more than one point. lways lways Sometimes ever Sometimes ever nswer Slide 38 / n angle that measures 90 degrees is a right angle. Slide 38 (nswer) / n angle that measures 90 degrees is a right angle. lways lways Sometimes ever Sometimes ever nswer Slide 39 / n angle that is less than 90 degrees is obtuse. Slide 39 (nswer) / n angle that is less than 90 degrees is obtuse. lways lways Sometimes ever Sometimes ever nswer

10 Slide 40 / n angle that is greater than 180 degrees is referred to as a reflex angle. Slide 40 (nswer) / n angle that is greater than 180 degrees is referred to as a reflex angle. lways lways Sometimes ever Sometimes ever nswer Slide 41 / 185 Slide 42 / 185 ongruence We learned earlier that if two line segments have the same length, they are congruent. ongruent ngles lso, all line segments with the same length are congruent. re these two segments congruent? b a Return to Table of ontents Slide 43 / 185 ongruence ow about two angles which are formed by two rays with common vertices. re all of those congruent? What would have to be the same for each of them to be congruent? Slide 44 / 185 ongruence If two angles have the same measure, they are congruent since they can be rotated and moved to overlap at every point.

11 Slide 45 / 185 ongruence owever, if their included angles do not have equal measure, they cannot be made to overlap at every point. or angles to be congruent, they need to have equal measures. Slide 46 / 185 ongruence owever, if their included angles do not have the same measure, they cannot be made to overlap at every point. or angles to be congruent, they need to have the same measure. re these two angles congruent? ere you can see clearly when we rotate the two angles from the previous slide, they do not have the same angle measure. Slide 47 / 185 Slide 48 / 185 ongruent ngles One way to indicate that two angles have the same measure is to label them with the same variable. or instance, labeling both of these angles x indicates that they have the same measure. ongruent ngles nother way to show angles are congruent is to mark the angle with a line. If there are 2 equal sets of angles, the second set could be marked with two lines. x x 14 Is congruent to? Slide 49 / Is congruent to? Slide 49 (nswer) / 185 Yes Yes o o nswer YS

12 Slide 50 / ongruent angles have the same measure. Slide 50 (nswer) / ongruent angles have the same measure. lways lways Sometimes ever Sometimes ever nswer 16 and are. Slide 51 / and are. Slide 51 (nswer) / 185 ongruent ongruent ot ongruent annot be determined ot ongruent nswer annot be determined 17 and are. Slide 52 / and are. Slide 52 (nswer) / 185 ongruent ongruent ot ongruent ot ongruent annot be determined annot be determined nswer

13 Slide 53 / 185 Slide 53 (nswer) / and are congruent. 18 and are congruent. True True alse annot be determined alse nswer annot be determined Slide 54 / 185 Slide 54 (nswer) / and are congruent. 19 and are congruent. True True alse alse nswer S Slide 55 / 185 Slide 56 / 185 djacent ngles ngles & ngle ddition Postulate djacent angles share a vertex and a side. The two angles are side by side, or adjacent. In this case, ngle is adjacent to ngle. Return to Table of ontents

14 Slide 57 / 185 ngle ddition Postulate Slide 58 / 185 ngle ddition Postulate The angle addition postulate says that the measures of two adjacent angles add together to form the measure of the angle formed by their exterior rays. In this case, ngle = ngle + ngle urther, it says that if any point lies in the interior of an angle, then the ray connecting that point to the vertex creates two adjacent angles that sum to the original angle. If lies in the interior of ngle then ngle + ngle = ngle Which yields the same result we had before. ngle = ngle + ngle Slide 59 / 185 ngle ddition Postulate xample Slide 59 (nswer) / 185 ngle ddition Postulate xample m PQS = 32 m SQR = 26 P 32 S m PQS = 32 m SQR = 26 nswer P 32 m PQR = 58 0 S Q R Q R What's the measure of PQR? What's the measure of PQR? Slide 60 / 185 ngle ddition Postulate xample Slide 60 (nswer) / 185 ngle ddition Postulate xample is in the interior of. If = (7x +11), = (15x + 24), and = (9x+204). Solve for x. (15x+24) is in the interior of. If = (7x +11), + = = (15x + 24), (7x +11) + (15x+24) = (9x+204) 22x + 35 = 9x+204 and = (9x+204). 13x + 35 = x = 169 Solve for x. x = 13 nswer (15x+24) (7x+11) (7x+11)

15 Slide 61 / iven m = 22 and m = 46. Slide 61 (nswer) / iven m = 22 and m = 46. ind m. 46 ind m. nswer = + = = Slide 62 / iven m OM = 64 and m O = 53. ind m M. Slide 62 (nswer) / iven m OM = 64 and m O = 53. ind m M O 64 M nswer M = O OM = O + M 64 = 53 + M M Slide 63 / iven m = 95 and m = 48. Slide 63 (nswer) / iven m = 95 and m = 48. ind m. ind m. 48 nswer

16 Slide 64 / iven m = 145 and m = 61. ind m. Slide 64 (nswer) / iven m = 145 and m = 61. ind m. nswer Slide 65 / iven m TRS = 61 and m SRQ = 153. ind m QRT. Slide 65 (nswer) / iven m TRS = 61 and m SRQ = 153. ind m QRT. S 61 R S 61 nswer R Q 153 Q T T Slide 66 / is in the interior of TUV. If m TUV = (10x + 72)⁰, m TU = (14x + 18)⁰ and m UV = (9x + 2)⁰ Solve for x. Slide 66 (nswer) / is in the interior of TUV. If m TUV = (10x + 72)⁰, m TU = (14x + 18)⁰ and 10x + 72 = 14x x + 2 m UV = (9x + 2)⁰ Solve for x. nswer 10x + 72 = 23x x = 52 x = 4

17 Slide 67 / is in the interior of. If m = (11x + 66)⁰, m = (5x + 3)⁰ and m = (13x + 7)⁰ Solve for x. Slide 67 (nswer) / is in the interior of. If m = (11x + 66)⁰, 11x + 66 = 5x x +7 m = (5x + 3)⁰ and 11x + 66 = 18x + 10 m = (13x + 7)⁰ 7x = 56 Solve for x. nswer x = 8 Slide 68 / is in the interior of QP. m QP = (3x + 44)⁰ Slide 68 (nswer) / is in the interior of QP. m QP = (3x + 44)⁰ m QP = (8x + 3)⁰ m Q= (5x + 1)⁰ Solve for x. m QP = (8x + 3)⁰ m Q= (5x + 1)⁰ Solve for x. nswer 3x + 44 = 8x x + 1 3x + 44 = 13x x = 40 x = 4 Slide 69 / The figure shows lines r, n, and p intersecting to form angles numbered 1, 2, 3, 4, 5, and 6. ll three lines lie in the same plane. ased on the figure, which of the individual statements would provide enough information to conclude that line r is perpendicular to line p? Select all that apply. m6 m 2 = = 90 m3 = m m1 + m6 = 90 Slide 69 (nswer) / The figure shows lines r, n, and p intersecting to form angles numbered 1, 2, 3, 4, 5, and 6. ll three lines lie in the same plane. ased on the figure, which of the individual statements would provide enough information to conclude that line r is perpendicular to line p? Select all that apply. nswer m6 m 2 = = 90 m3 = m m1 + m6 = 90 m3 + m4 = 90 m3 + m4 = 90 rom PR sample test m4 + m5 = 90 rom PR sample test m4 + m5 = 90

18 Slide 70 / 185 Slide 71 / 185 Protractors Protractors ngles are measured in degrees, using a protractor. very angle has a measure from 0 to 180 degrees. ngles can be drawn in any size. Return to Table of ontents Slide 72 / 185 Protractors Slide 73 / 185 Protractors is a 23 degree angle The measure of is 23 degrees is a 118 angle. The measure of is 118. Slide 74 / 185 Slide 75 / 185 Protractors Protractors rom our prior results we know that ngle = and ngle = So, the ngle ddition Postulate tells us that ngle must be what? Without those prior results, we could just read the values of and 23 0 from the protractor to get the included angle to be 95 0.

19 29 What is the m? Slide 76 / What is the m? Slide 76 (nswer) / o 39 o 54 o 130 o 180 o 54 o 130 o 180 o nswer Slide 77 / 185 Slide 77 (nswer) / What is the m 30 What is the m 39 o 39 o 54 o 130 o 180 o 54 o 130 o 180 o nswer Slide 78 / 185 Slide 78 (nswer) / What is the m? 31 What is the m? 141 o 141 o 54 o 39 o 15 o 54 o 39 o 15 o nswer

20 32 What is the m? Slide 79 / What is the m? Slide 79 (nswer) / o 54 o 76 o 90 o 130 o 76 o 90 o 130 o nswer Slide 80 / 185 Slide 80 (nswer) / What is the m? 33 What is the m? 39 o 39 o 51 o 51 o 90 o 141 o 90 o 141 o nswer Slide 81 / 185 Slide 81 (nswer) / P = 34 P = M M nswer 32 o P O P O

21 Slide 82 / 185 Slide 82 (nswer) / PM = 35 PM = M nswer M 90 P O P O Slide 83 / 185 Slide 83 (nswer) / PO = 36 PO = M nswer M 180 P O P O Slide 84 / 185 Slide 84 (nswer) / P = 37 P = M nswer M 63 P O P O

22 Slide 85 / 185 Slide 85 (nswer) / P = 38 P = M nswer M 135 P O P O Slide 86 / 185 Slide 86 (nswer) / M = 39 M = M nswer M o P O P O Slide 87 / 185 Slide 87 (nswer) / M = 40 M = M nswer M o P O P O

23 Slide 88 / 185 Slide 88 (nswer) / = 41 = M nswer M o P O P O Slide 89 / 185 Slide 89 (nswer) / = 42 = M nswer M o P O P O Slide 90 / 185 Slide 91 / 185 omplementary ngles omplementary angles are angles whose sum measures Special ngle Pairs One such angle is said to complement the other. They may be adjacent, but don't need to be. 25 o Return to Table of ontents 65 o 25 o omplementary adjacent 65 o omplementary nonadjacent

24 Slide 92 / 185 omplementary ngles djacent complementary angles form a right angle. Slide 93 / What is the complement of an angle whose measure is 72 0? ngle and ngle are complementary since they comprise ngle, which is a right angle. Slide 93 (nswer) / What is the complement of an angle whose measure is 72 0? Slide 94 / What is the complement of an angle whose measure is 28 0? nswer 18 0 Slide 94 (nswer) / What is the complement of an angle whose measure is 28 0? Slide 95 / 185 xample nswer 62 0 Two angles are complementary. The larger angle is twice the size of the smaller angle. What is the measure of both angles? et x = the smaller angle and the larger angle = 2x.

25 Slide 95 (nswer) / 185 xample Two angles are Since complementary. the angles are complementary we know The larger angle is twice the size of the smaller angle. their sum must equal 90 What is the measure degrees. of both angles? nswer 90 = 2x + x 90 = 3x et x = the smaller angle and 30 the = x larger angle = 2x. Slide 96 / n angle is 34 more than its complement. What is its measure? Slide 96 (nswer) / n angle is 34 more than its complement. What is its measure? Slide 97 / n angle is 14 less than its complement. What is the angle's measure? nswer angle = complement + 34 angle = (90 - x) + 34 x = 90 - x +34 2x = 124 x = 62 Slide 97 (nswer) / n angle is 14 less than its complement. What is the angle's measure? Slide 98 / 185 Supplementary ngles Supplementary angles are angles whose sum measures nswer angle = complement - 14 angle = (90 - x) - 14 x = 90 - x x = x = 76 x = 38 Supplementary angles may be adjacent, but don't need to be. One angle is said to supplement the other. 25 o 155o 25 o Supplementary adjacent a.k.a. inear Pair 155 o Supplementary nonadjacent

26 Slide 99 / 185 Supplementary ngles ny two angles that add to a straight angle are supplementary. Slide 100 / What is the supplement of an angle whose measure is 72 0? Or, two adjacent angles whose exterior sides are opposite rays, are supplementary. If ngle is a straight angle, its measure is Then ngle and ngle are supplementary since their measures add to Slide 100 (nswer) / What is the supplement of an angle whose measure is 72 0? Slide 101 / What is the supplement of an angle whose measure is 28 0? nswer Slide 101 (nswer) / What is the supplement of an angle whose measure is 28 0? Slide 102 / The measure of an angle is 98 0 more than its supplement. What is the measure of the angle? nswer 152 0

27 Slide 102 (nswer) / 185 Slide 103 / The measure of an angle is 98 0 more than its supplement. What is the measure of the angle? 50 n measure of angle is 74 less than its supplement. What is the angle? nswer angle = (180 - x) + 98 x = x x = 278 x = 139 Slide 103 (nswer) / 185 Slide 104 / n measure of angle is 74 less than its supplement. 51 The measure of an angle is 26 more than its supplement. What is the angle? nswer angle = supplement - 74 x = (180 - x) x = x = 106 x = 53 What is the angle? Slide 104 (nswer) / The measure of an angle is 26 more than its supplement. What is the angle? nswer angle = supplement + 26 x = (180 - x) x = x = 206 x = 103 Slide 105 / 185 Vertical ngles Vertical ngles are two angles whose sides form two pairs of opposite rays Whenever two lines intersect, two pairs of vertical angles are formed. & are vertical angles, and & are vertical angles.

28 Slide 106 / 185 Vertical ngles Slide 107 / 185 Vertical ngles & are vertical angles & are vertical angles. We can prove some important propeties about these three special cases: angles which are complementary, supplementary or vertical. Two column proofs use one column to make a statement and the column next to it to provide the reason, as shown below. We're going to use those a lot, so we're going to use this example to both prove three theorems. Slide 108 / 185 Slide 109 / 185 Two olumn Proofs Proofs Special ngles Proofs all start out with a goal: what it is we are trying to prove. They are not open-ended explorations, but are directed towards a specific end. We know the last statement of every proof when we start, it is what we are trying to prove. We don't know the reason in advance. Return to Table of ontents Slide 110 / 185 omplementary ngles Theorem Theorem: ngles which are complementary to the same angle are equal. Slide 111 / 185 omplementary ngles Theorem Theorem: ngles which are complementary to the same angle are equal. iven: ngles 1 and 2 are complementary ngles 1 and 3 are complementary Prove: m 2 = m 3 Statement 1 ngles 1 and 2 are complementary ngles 1 and 3 are complementary Reason 1 iven What do we know about the sum of the measures of complementary angles?

29 Slide 112 / 185 omplementary ngles Theorem Slide 113 / 185 omplementary ngles Theorem Statement 2 m 1 + m 2 = 90 m 1 + m 3 = 90 Reason 2 efinition of complementary angles Statement 3 m 1 + m 2 = m 1 + m 3 Reason 3 Substitution property of equality ow, we can set the left sides equal by substituting for 90 nd, now subtract m 1 from both sides. Slide 114 / 185 omplementary ngles Theorem Slide 115 / 185 omplementary ngles Theorem iven: ngles 1 and 2 are complementary ngles 1 and 3 are complementary Prove: m 2 = m 3 Statement 4 m 2 = m 3 Reason 4 Subtraction property of equality Which is what we set out to prove Statement ngles 1 and 2 are complementary ngles 1 and 3 are complementary m 1 + m 2 = 90 m 1 + m 3 = 90 m 1 + m 2 = m 1 + m 3 m 2 = m 3 Reason iven efinition of complementary angles Substitution Property of quality Subtraction Property of quality Slide 116 / 185 Slide 117 / 185 Supplementary ngles Theorem Supplementary ngles Theorem Theorem: ngles which are supplementary to the same angle are equal. iven: ngles 1 and 2 are supplementary ngles 1 and 3 are supplementary iven: ngles 1 and 2 are supplementary ngles 1 and 3 are supplementary Prove: m 2 = m 3 This is so much like the last proof, that we'll do this by just examining the total proof. Prove: m 2 = m 3 Statement ngles 1 and 2 are supplementary ngles 1 and 3 are supplementary m 1 + m 2 = 180 m 1 + m 3 = 180 m 1 + m 2 = m 1 + m 3 m 2 = m 3 Reason iven efinition of supplementary angles Substitution property of equality Subtraction property of equality

30 Slide 118 / 185 Vertical ngles Theorem Vertical angles have equal measure iven: line and line are straight lines that intersect at Point and form angles 1, 2, 3 and 4 Slide 119 / 185 Vertical ngles Theorem The first statement will focus on what we are given which makes this situation unique. In this case, it's just the ivens. Prove: m 1 = m 3 and m 2 = m 4 Slide 120 / 185 Vertical ngles Theorem Statement 1 line and line are straight lines that intersect at Point and form angles 1, 2, 3 and Reason 1 iven Then, we know we want to know something about the relationship between the pairs of vertical angles: 1 & 3 and 2 & 4. Slide 121 / We know that angles. 1 & 4 are supplementary 1 & 3 are supplementary 2 & 3 are supplementary 3 & 4 are supplementary ll of the above What do you know about these four angles that the givens can help us with. Slide 121 (nswer) / We know that angles. 1 & 4 are supplementary 1 & 3 are supplementary 2 & 3 are supplementary 3 & 4 are supplementary ll of the above nswer Slide 122 / 185 Vertical ngles Theorem Statement 2 1 & 2 are supplementary 1 & 4 are supplementary 2 & 3 are supplementary 3 & 4 are supplementary Reason 2 ngles that form a linear pair are supplementary What do you know about two angles which are supplementary to the same angle, like 2 & 4 which are both supplements of 1?

31 Slide 123 / 185 Vertical ngles Theorem Slide 124 / 185 Vertical ngles Theorem Statement 2 1 & 2 are supplementary 1 & 4 are supplementary 2 & 3 are supplementary 3 & 4 are supplementary Reason 2 ngles that form a linear pair are supplementary et's look at the fact that 2 & 4 are both supplementary to 1 and that 1 & 3 are both supplementary to 4, since that relates to the vertical angles we're interested in. Statement Slide 125 / 185 Vertical ngles Theorem iven: and are straight lines that intersect at Point and form angles 1, 2, 3 and 4 Prove: m 1 = m 3 and m 2 = m 4 Reason line and line are straight lines that intersect at Point and iven form angles 1, 2, 3 and Statement 3 m 1 = m 3 m 2 = m 4 Reason 3 Two angles supplementary to the same angle are equal ut those are the pairs of vertical angles which we set out to prove are equal. So, our proof is complete: vertical angles are equal Slide 126 / 185 Vertical ngles Theorem We have proven that vertical angles are congruent. This becomes a theorem we can use in future proofs. lso, we can solve problems with it. 1 & 2 are supplementary 1 & 4 are supplementary 2 & 3 are supplementary 3 & 4 are supplementary m 1 = m 3 and m 2 = m 4 ngles that form a linear pair are supplementary Two angles supplementary to the same angle are equal Slide 127 / 185 Vertical ngles iven: m = 55 o, solve for x, y and z. iven: m = 55 o Slide 128 / 185 Vertical ngles x o 55 o We know that x + 55 = 180 0, since they are supplementary. nd that y = 55 0, since they are vertical angles. nd that x = z for the same reason. y o zo 125 o 55 o 55 o 125 o

32 Slide 129 / 185 xample Slide 130 / What is the measure of angle 1? ind m 1, m 2 & m 3. xplain your answer. 36 o m 1 = 180 m 1 = 144 o inear pair angles are supplementary 77 o 103 o 113 o none of the above m 2 = 36 o ; Vertical angles are congruent (original angle & m 2) m 3 = 144 o ; Vertical angles are congruent (m 1 & m 3) o Slide 130 (nswer) / What is the measure of angle 1? Slide 131 / What is the measure of angle 2? 77 o 103 o 113 o nswer none of the above 77 o 103 o 113 o none of the above 1 77 o 1 77 o Slide 131 (nswer) / What is the measure of angle 2? Slide 132 / What is the measure of angle 3? 77 o 103 o 113 o nswer none of the above 1 77 o o 103 o 113 o none of the above o

33 Slide 132 (nswer) / What is the measure of angle 3? Slide 133 / What is the measure of angle 4? 77 o 103 o 113 o nswer none of the above 1 77 o 112 o 78 o 102 o none of the above o 6 5 Slide 133 (nswer) / What is the measure of angle 4? 112 o 78 o 102 o nswer none of the above ) m < 4 = 68 o Slide 134 / What is the measure of angle 5? 112 o 68 o 102 o none of the above o o 6 5 Slide 134 (nswer) / What is the measure of angle 5? 58 What is the m 6? Slide 135 / o 68 o 102 o nswer none of the above 102 o 78 o 112 o none of the above o o 6 5

34 58 What is the m 6? Slide 135 (nswer) / 185 Slide 136 / 185 xample 102 o 78 o 112 o none of the above nswer ind the value of x. The angles shown are vertical, so they are congruent o [This 6 object 5is a pull (14x + 7) o (13x + 16) o Slide 136 (nswer) / 185 xample Slide 137 / 185 xample ind the value of x. The angles shown are vertical, so they are congruent. ind the value of x. The angles shown are supplementary nswer 13x + 16 = 14x x -13x 16 = x = x (13x + 16) o (2x + 8) o (3x + 17) o (14x + 7) o Slide 137 (nswer) / 185 xample 59 ind the value of x. Slide 138 / 185 ind the value of x. nswer (2x + 8) o The angles shown are supplementary 2x x + 17 = 180 5x + 25 = 180 (3x + 17) o x = x = o (2x - 5) o

35 59 ind the value of x. Slide 138 (nswer) / ind the value of x. Slide 139 / nswer 85 o (2x - 5) o o (6x + 3) o 60 ind the value of x. Slide 139 (nswer) / ind the value of x. Slide 140 / nswer o (6x + 3) o (9x - 4) o 122 o 61 ind the value of x. Slide 140 (nswer) / ind the value of x. Slide 141 / nswer (9x - 4) o 122 o (7x + 54) o 42o

36 Slide 141 (nswer) / 185 Slide 142 / ind the value of x nswer ngle isectors (7x + 54) o 42o Return to Table of ontents Slide 143 / 185 Slide 144 / 185 n angle bisector is a ray or line which starts at the vertex and cuts an angle into two equal halves ngle isector X ray X bisects inding the missing measurement. xample: is bisected by ray. ind the measures of the missing angles. isect means to cut it into two equal parts. The 'bisector' is the thing doing the cutting. The angle bisector is equidistant from the sides of the angle when measured along a segment perpendicular to the sides of the angle. 52 o Slide 144 (nswer) / 185 Slide 145 / 185 inding the missing measurement. xample: is bisected by ray. ind the measures of the missing angles. 63 is bisected by. The m = ind the measures of the missing angles. nswer m = 52 o m = 2(52) = 104 o 56 o 52 o

37 Slide 145 (nswer) / is bisected by. The m = ind the measures of the missing angles. Slide 146 / MO bisects M. ind the value of x. nswer 56 o m = 56/2 = 28 o m = 28 o M (x + 10) o O (3x - 20) o Slide 146 (nswer) / 185 Slide 147 / MO bisects M. ind the value of x. 65 Ray P bisects MO iven that MP = 57o, what is MO? M m MO =m OM x + 10 = 3x x -x (x + 10) o 10 = O2x - 20 (3x - 20) o = 2x [This = xobject is a pull nswer int: click to reveal What does bisect mean? raw & label a picture. Slide 147 (nswer) / 185 Slide 148 / Ray P bisects MO iven that MP = 57o, what is MO? 66 Ray RT bisects QRS iven that QRT = 78o, what is QRS? nswer m MO = 2(57) = 114 o int: click to reveal What does bisect mean? raw & label a picture.

38 Slide 148 (nswer) / Ray RT bisects QRS iven that QRT = 78o, what is QRS? Slide 149 / Ray VY bisects UVW. iven that UVW = 165o, what is UVY? nswer m QRS = 2(78) = 156 o Slide 149 (nswer) / Ray VY bisects UVW. iven that UVW = 165o, Slide 150 / Ray bisects. ind the value of x. what is UVY? nswer m UVY = 165/2 = 82.5 o (7x + 3) o (11x - 25) o Slide 150 (nswer) / 185 Slide 151 / Ray bisects. ind the value of x. 69 Ray bisects. ind the value of x. (7x + 3) o nswer 7x + 3 = 11x = 4x = 4x 7 = x (9x - 17) o (11x - 25) o (3x + 49) o

39 Slide 151 (nswer) / Ray bisects. ind the value of x. Slide 152 / Ray bisects I. ind the value of x. (9x - 17) o nswer 9x - 17 = 3x x - 17 = 49 6x = 66 x = 11 I (7x + 1) o (3x + 49) o (12x - 19) o Slide 152 (nswer) / 185 Slide 153 / Ray bisects I. ind the value of x. I nswer (7x + 1) o 7x + 1 = 12x = 5x = 5x 4 = x ocus & ngle onstructions (12x - 19) o Return to Table of ontents Slide 154 / 185 onstructing ongruent ngles iven: onstruct: such that Our approach will be based on the idea that the measure of an angle is how much we would have rotate one ray it overlap the other. The larger the measure of the angle, the farther apart they are as you move away from the vertex. Slide 155 / 185 onstructing ongruent ngles So, if we go out a fixed distance from the vertex on both rays and draw points there, the distance those points are apart from one another defines the measure of the angle. The bigger the distance, the bigger the measure of the angle. If we construct an angle whose rays are the same distance apart at the same distance from the vertex, it will be congruent to the first angle.

40 Slide 156 / 185 onstructing ongruent ngles 1. raw a reference line with your straight edge. Place a reference point () to indicate where your new ray will start on the line. Slide 157 / 185 onstructing ongruent ngles 2. Place the compass point on the vertex and stretch it to any length so long as your arc will intersect both rays. 3. raw an arc that intersects both rays of. (This defines a common distance from the vertex on both rays since the arc is part of a circle and all its points are equidistant from the center of the circle.) Slide 158 / 185 Slide 159 / 185 onstructing ongruent ngles onstructing ongruent ngles 4. Without changing the span of the compass, place the compass tip on your reference point and swing an arc that goes through the line and above it. (This defines that same distance from the vertex on both our reference ray and the ray we will draw as we used for the original angle.) 5. ow place your compass where the arc intersects one ray of the original angle and set it so it can draw an arc where it crosses the other ray. (This defines how far apart the rays are at that distance from the vertex.) Slide 160 / 185 Slide 161 / 185 onstructing ongruent ngles onstructing ongruent ngles 6. Without changing the span of the compass place the point of the compass where the first arc crosses the first ray and draw an arc that intersects the arc above the ray. 6. ow, use your straight edge to draw the second ray of the new angle which is congruent with the first angle. (This will make the separation between the rays the same at the same distance from the new vertex as was the case for the original angle.)

41 Slide 162 / 185 onstructing ongruent ngles It should be clear that these two angles are congruent. Ray would have to be rotated the same amount to overlap Ray as would Ray to overlap Ray. Slide 163 / 185 onstructing ongruent ngles We can confirm that by putting one atop the other. otice that where we place the points is not relevant, just the shape of the angle indicates congruence. Slide 164 / 185 Slide 164 (nswer) / 185 Try this! Try this! onstruct a congruent angle on the given line segment. 5) P Q onstruct a congruent angle on The the file given for line the segment. "Try This!" problems is located on the 5) T website: geometry/points-lines-andplanes/ P under "andouts". Teacher otes Q R R Slide 165 / 185 Try this! onstruct a congruent angle on the given line segment. 6) Slide 166 / 185 Video emonstrating onstructing ongruent ngles using ynamic eometric Software lick here to see video

42 Slide 167 / 185 Slide 168 / 185 onstructing ngle isectors s we learned earlier, an angle bisector divides an angle into two adjacent angles of equal measure. ngle isectors & onstructions To create an angle bisector we will use an approach similar to that used to construct a congruent angle, since, in this case, we will be constructing two congruent angles. U Return to Table of ontents V W Slide 169 / 185 onstructing ngle isectors 1. With the compass point on the vertex, draw an arc that intersects both rays. (This will establish a fixed distance from the vertex on both rays. Slide 170 / 185 onstructing ngle isectors 2. Without changing the compass setting, place the compass point on the intersection of each arc and ray and draw a new arc such that the two new arcs intersect in the interior of the angle. (This fixes the distance from each original ray to the new ray to be the same, so that the two new angles will be congruent.) U U V W V W Slide 171 / 185 onstructing ngle isectors 3. With a straightedge, draw a ray from the vertex through the intersection of the arcs and label that point. ecause we know that the distance of each original ray to the new ray is the same, at the same distance from the vertex, we know the measures of the new angles is the same and that m UVX = m XVW U isect the angle 7) Slide 172 / 185 Try This! X V W

43 Slide 172 (nswer) / 185 Try This! Slide 173 / 185 Try This! isect the angle isect the angle 7) Teacher otes The file for the "Try This!" problems is located on the T website: geometry/points-lines-andplanes/ under "andouts". 8) Slide 174 / 185 onstructing ngle isectors w/ string, rod, pencil & straightedge verything we do with a compass can also be done with a rod and string. In both cases, the idea is to mark a center (either the point of the compass or the rod) and then draw an part of a circle by keeping a fixed radius (with the span of the compass or the length of the string. Slide 175 / 185 onstructing ngle isectors w/ string, rod, pencil & straightedge 1. With the rod on the vertex, draw an arc across each side. U V W Slide 176 / 185 onstructing ngle isectors w/ string, rod, pencil & straightedge 2. Place the rod on the arc intersections of the sides & draw 2 arcs, one from each side showing an intersection point. U Slide 177 / 185 onstructing ngle isectors w/ string, rod, pencil & straightedge 3. With a straightedge, connect the vertex to the arc intersections. abel your point. m UVX = m XVW U X V W V W

44 Slide 178 / 185 Try This! isect the angle with string, rod, pencil & straightedge. 9) Slide 179 / 185 Try This! isect the angle with string, rod, pencil & straightedge. 10) Slide 180 / 185 onstructing ngle isectors by olding 1. On patty paper, create any angle of your choice. Make it appear large on your patty paper. abel the points, &. Slide 181 / 185 onstructing ngle isectors by olding 2. old your patty paper so that ray lines up with ray. rease the fold. Slide 182 / 185 onstructing ngle isectors by olding 3. Unfold your patty paper. raw a ray along the fold, starting at point. raw and label a point on your ray. isect the angle with folding. 11) Slide 183 / 185 Try This!

45 Slide 184 / 185 Slide 185 / 185 Try This! isect the angle with folding. 12) Videos emonstrating onstructing ngle isectors using ynamic eometric Software lick here to see video using a compass and segment tool lick here to see video using the menu options