Section 5: Introduction to Polygons Part 2

Transcription

1 Section 5: Introduction to Polygons Part 2 Topic 1: Compositions of Transformations of Polygons Part Topic 2: Compositions of Transformations of Polygons Part Topic 3: Symmetries of Regular Polygons Topic 4: Congruence and Similarity of Polygons Part Topic 5: Congruence and Similarity of Polygons Part Visit MathNation.com or search "Math Nation" in your phone or tablet's app store to watch the videos that go along with this workbook! 107

2 The following Mathematics Florida Standards will be covered in this section: G-CO Given a rectangle, parallelogram, trapezoid, or regular polygon, describe the rotations and reflections that carry it onto itself. G-CO Given a geometric figure and a rotation, reflection, or translation, draw the transformed figure. Specify a sequence of transformations that will carry a given figure onto itself. G-CO Use geometric descriptions of rigid motions to transform figures and to predict the effect of a given rigid motion on a given figure; given two figures, use the definition of congruence in terms of rigid motions to decide if they are congruent. G-CO Use the definition of congruence in terms of rigid motions to show that two triangles are congruent if and only if corresponding pairs of sides and corresponding pairs of angles are congruent. G-SRT Given two figures, use the definition of similarity transformations to decide if they are similar; explain using similarity transformations the meaning of similarity for triangles as the equality of all corresponding pairs of angles and the proportionality of all corresponding pairs of sides. 108

3 Section 5: Introduction to Polygons Part 2 Section 5 Topic 1 Compositions of Transformations of Polygons Part 1 What do you think composition of transformations means? Consider the following double reflections. B A C Identify and describe a real-life example. C C A B B A Consider the following glide reflections. What do you notice about the double reflections? M O C B A B A C G E G E v M O What is a composition of isometries? What do you notice about the glide reflections? 109

4 Consider the following figure. Reflect the figure over = 1, then rotate the figure 270 clockwise about the origin. Consider the figure below. Consider the following figure. Dilate the figure at the origin with a scale factor of 4 and then reflect the figure over =. 5 If you are limited by three transformations, describe what type(s) of transformations or compositions will carry the polygon onto itself. Do these transformations represent composition of isometries? Justify your answer. 110

5 Section 5 Topic 2 Compositions of Transformations of Polygons Part 2 Let s Practice! Try It! 2. Consider the figure below and the following rotation. Rectangle PPPPPPPP is rotated 270 counterclockwise around the origin and then reflected across the -axis. 1. Consider the following information. A pre-image of SSSSSSSS with coordinates SS 7, 2, PP 0, 9, OO 6, 5, and TT(1, 12) H T a. If we reflect SSSSSSSS over the -axis then rotate it 90 counterclockwise about the origin, what are the coordinates of SS"PP"OO"TT"? Write each answer in the space provided below. P A SS(7, 2) SS (, ) SS"(, ) PP(0, 9) PP (, ) PP"(, ) OO( 6, 5) OO (, ) OO"(, ) TT(1, 12) TT (, ) TT"(, ) b. If you take SS"PP"OO"TT" and dilate it by a scale factor of 3 centered at the origin, what are the coordinates of SS PP OO TT? Justify your answer. Tatum argues that the image created above will be the same as the pre-image. Marla refutes the answer by arguing that the images will not be the same. Who is correct? Justify your answer. 111

6 BEAT THE TEST! 1. Point PP"( 9,0) is a vertex of triangle PP"II"EE". The original image was rotated 90 clockwise and then translated, ( 8, + 5). What are the coordinates of the original image s point PP before the composition of transformations? A B C 1, 5 0, 4 1, 5 D (5, 1) 2. Consider the following polygon after a composition of transformations represented by the dashed lines below. Which composition of isometries did the polygon have? A A reflection over the -axis and a translation ( + 7, + 1). B A reflection over = 1 and a translation ( + 7, ). C A translation ( + 8, 3) and a rotation of 90 clockwise about (1, 1). D A translation ( + 10, ) and a reflection over =. 112

7 Section 5 Topic 3 Symmetries of Regular Polygons Which of the following are symmetrical? Circle the figure(s) that are symmetrical. Consider the rectangle shown below in the coordinate plane. We need to identify the equation of the line that maps the figure onto itself after a reflection across that line. What do you think it means to map a figure onto itself? Reflect the image across the line = 1. Does the transformation result in the original pre-image? Reflect the image across the line = 1. Does the transformation result in the original pre-image? Draw a figure and give an example of a single transformation that carries the image onto itself. Reflect the image across the line = 1. Does the transformation result in the original pre-image? Reflect the image across the line = 2. Does the transformation result in the original pre-image? The equations of the lines that map the rectangle above onto itself are and. 113

8 Reflecting a regular nn-gon across a line of symmetry carries the nn-gon onto itself. Let s explore lines of symmetry. In regular polygons, if nn is odd, the lines of symmetry will pass through a vertex and the midpoint of the opposite side. Draw the lines of symmetry on the polygon below. Let s Practice! 1. Consider the trapezoid below. In regular polygons, if nn is even, there are two scenarios. Ø Ø The lines of symmetry will pass through two opposite vertices. The lines of symmetry will pass through the midpoints of two opposite sides. Draw the lines of symmetry on the polygon below. Which line will carry the figure onto itself? A = 1 B = 2 C = 4 D = 6 114

9 Try It! 2. Which of the following transformations carries this regular polygon onto itself? Rotations also carry a geometric figure onto itself. What rotations will carry a regular polygon onto itself? b aa c About which location do you rotate a figure in order to carry it onto itself? d What rotation would carry this regular hexagon onto itself? A Reflection across line aa B Reflection across line bb C Reflection across line cc D Reflection across line dd 3. How many ways can you reflect each of the following figures onto itself? a. Regular heptagon: b. Regular octagon: Rotating a regular nn-gon by a multiple of WXY Z carries the nn-gon onto itself. 115

10 Let s Practice! 4. Consider the regular octagon below with center at the origin and a vertex at (4, 0). Try It! 5. Which rotations will carry this regular polygon onto itself? 6. Consider the two rectangles below. Describe a rotation that will map this regular octagon onto itself. The degree of rotation that maps each figure onto itself is a rotation degrees about the point (, ). 116

11 BEAT THE TEST! 1. Which of the following transformations carry this regular polygon onto itself? Select all that apply. Section 5 Topic 4 Congruence and Similarity of Polygons Part 1 Consider the figures below. t o o o o o o Reflection across line tt Reflection across its base Rotation of 40 counterclockwise Rotation of 90 counterclockwise Rotation of 120 clockwise Rotation of 240 counterclockwise Explain which figures are congruent, if any. Make observations from the figures above to state properties of congruent polygons. Ø Ø Ø Congruent polygons have the same number of and. Corresponding of congruent polygons are congruent. Corresponding interior of congruent polygons are congruent. 117

12 Let s Practice! Consider the following similar shapes. 1. Which coordinates will produce a rectangle that is congruent to the one shown below? Why do we classify these shapes as similar instead of congruent? A 2, 4, 0, 4, 2, 14, 0, 14 B 6, 4, 2, 4, 6, 10, 2, 10 C 6, 8, 0, 8, 6, 4, 0, 4 D 0, 0, 4, 0, 0, 10, (10, 4) Make observations from the figures above to state properties of similar polygons. Try It! 2. Romeo drew a quadrilateral with interior angles measuring 72, 136, and 110. Juliet drew a quadrilateral that is congruent to Romeo s. Which of the following is one of the angle measures of Juliet s quadrilateral? A 42 B 52 C 70 D 108 Ø Ø Ø Similar polygons have the same number of and. Corresponding interior of similar polygons are congruent. Corresponding of similar polygons are proportional. 118

13 Consider the polygons on the coordinate plane below. Section 5 Topic 5 Congruence and Similarity of Polygons Part 2 Let s Practice! A B E F 1. Parallelograms AAAAAAAA and PPPPPPPP are similar. D C H G A B P Q 9 yd 54 yd D yd C Based on the two similar squares above, name the properties of similar polygons, and give the justifications that prove the figures are similar. S a. What is the scale factor from PPPPPPPP to AAAAAAAA? R # Properties Justifications b. What is the length of RRRR?

14 2. Mrs. Kemp s rectangular garden has a length of 20 meters and a width of 15 meters. Her neighbor, Mr. Pippen, has a garden similar in shape with a scale factor of 3. a. What is the width of Mr. Pippen s garden? Try It! 3. A right triangle has a base of 11 yards and a height of 7 yards. If you were to construct a similar but not congruent right triangle with area of 616 square yards, what would the dimensions of the new triangle be? b. How do the areas of the gardens relate to one another? 4. Triangle TTTTTT is similar to triangle GGGGGG. TTTT is 10 inches long, OOOO is 6 inches long, GGGG is 16 inches long, and GGGG is 13.8 inches long. How long is TTTT? Each corresponding side of a polygon can be multiplied by the scale factor to get the length of its corresponding side on a similar polygon. Then, the ratio of the areas is the square of the scale factor while the ratio of perimeters is the scale factor. 120

15 5. What conjectures can you make if two similar polygons have a similarity ratio of 1? Draw an example to justify your conjectures. 6. Which quadrant has two similar polygons? Justify your answer. 121

16 BEAT THE TEST! 1. Which transformation would result in the perimeter of a polygon being different from the perimeter of its preimage? 3. In triangle AAAACC, mm AA = 90 and mm BB = 35. In triangle DDDDDD, mm EE = 35 and mm FF = 55. Are the triangles similar? Prove your answer. A (, ) (, ) B (, ) (, ) C (, ) (3, 3) D (, ) ( 3, + 1) 2. The areas of two similar polygons are in the ratio 25: 81. Find the ratio of the corresponding sides. 4. Four of the angle measures of a pentagon that Kym drew are 100, 120, 120, and 140. Her brother drew a pentagon that was congruent to Kym s. Which answer below represents one of the angle measures of her brother s pentagon? A 30 B 42 C 60 D 160 Test Yourself! Practice Tool Great job! You have reached the end of this section. Now it s time to try the Test Yourself! Practice Tool, where you can practice all the skills and concepts you learned in this section. Log in to Math Nation and try out the Test Yourself! Practice Tool so you can see how well you know these topics! 122