Squares and Rectangles. Properties of Squares and Rectangles

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1 Squares and Rectangles Properties of Squares and Rectangles.1 Learning Goals In this lesson, you will: Prove the Perpendicular/Parallel Line Theorem. Construct a square and a rectangle. Determine the properties of a square and rectangle. Prove the properties of a square and a rectangle. Solve problems using the properties of a square and a rectangle. Key Term Perpendicular/Parallel Line Theorem In 20, a technology company unveiled what was billed at the time as the world s largest plasma TV. This monster of a TV measured 12 2 feet across the diagonal 3 (152 inches long) and displayed nearly 9 million pixels in HD and, if necessary, 3D. Just two years earlier, the same company released a 3-inch version (89.3 inches long) which you could buy for a mere $70,000. How much would you estimate the 152-inch TV cost if the company set its prices based on the total viewing areas for their TVs? 741

2 Problem 1 Know the Properties or Be Square!? Prove: 1 i 2 A quadrilateral is a four-sided polygon. A square is a quadrilateral with four right angles and all sides congruent. Quadrilaterals have different properties that are directly related to the measures of their interior angles and their side lengths. Perpendicular lines and right angles are useful when proving properties of certain quadrilaterals. 1. Ramira says that if two lines are perpendicular to the same line, then the two lines are parallel to each other. Is Ramira correct? If she is correct, complete the proof to justify the reasoning, or state why she is not correct. Given: 1 ' 3 ; 2 ' Remember, in proofs, start with the Given statement or statements. 742 Chapter Properties of Quadrilaterals

3 The Perpendicular/Parallel Line Theorem states: If two lines are perpendicular to the same line, then the two lines are parallel to each other. 2. Draw a square with two diagonals. Label the vertices and the intersection of the diagonals. List all of the properties you know to be true. A diagonal of a polygon is a line segment that connects two non-adjacent vertices. 3. Use AB to construct square ABCD with diagonals AC and BD intersecting at point E. A B.1 Properties of Squares and Rectangles 743

4 4. Prove the statement DAB CBA. Given: Square ABCD with diagonals AC and BD intersecting at point E Prove: DAB CBA D C E A B 5. Do you have enough information to conclude AC BD? Explain your reasoning. You have just proven a property of a square: that its diagonals are congruent. You can now use this property as a valid reason in future proofs. 744 Chapter Properties of Quadrilaterals

5 6. Prove the statement DA i CB and DC i AB. Given: Square ABCD Prove: DA i CB and DC i AB D C A B 7. If a parallelogram is a quadrilateral with opposite sides parallel, do you have enough information to conclude square ABCD is a parallelogram? Explain your reasoning. You have just proven another property of a square: that its opposite sides are parallel. You can now use this property as a valid reason in future proofs..1 Properties of Squares and Rectangles 745

6 8. Prove the statement DE BE and CE AE. Given: Square ABCD with diagonals AC and BD intersecting at point E Prove: DE BE and CE AE D C E A B 9. Do you have enough information to conclude the diagonals of a square bisect each other? Explain your reasoning. You have just proven another property of a square: that its diagonals bisect each other. You can now use this property as a valid reason in future proofs. 746 Chapter Properties of Quadrilaterals

7 . Prove that the diagonals of a square bisect the vertex angles. Use square ABCD in Question Prove that the diagonals of a square are perpendicular to each other. Use square ABCD in Question 8..1 Properties of Squares and Rectangles 747

8 Problem 2 The Rectangle A rectangle is a quadrilateral with opposite sides congruent and all angles congruent. 1. Draw a rectangle with two diagonals. Label the vertices and the intersection of the two diagonals. List all of the properties you know to be true. A square is also a rectangle. But, don t draw a square. 2. Use RE to construct rectangle RECT with diagonals RC and ET intersecting at point A. Do not construct a square. R E 748 Chapter Properties of Quadrilaterals

9 3. Prove the statement RCT ETC. Given: Rectangle RECT with diagonals RC and ET intersecting at point A Prove: RCT ETC R E A T C 4. Do you have enough information to conclude RT EC? Explain your reasoning..1 Properties of Squares and Rectangles 749

10 5. Describe how you could prove the second pair of opposite sides of the rectangle are congruent. 6. Do you have enough information to conclude rectangle RECT is a parallelogram? Explain your reasoning. 7. Do you have enough information to conclude the diagonals of a rectangle are congruent? Explain your reasoning. 8. Do you have enough information to conclude the diagonals of a rectangle bisect each other? Explain your reasoning. 750 Chapter Properties of Quadrilaterals

11 Problem 3 Using Tools 1. Ofelia is making a square mat for a picture frame. How can she make sure the mat is a square using only a ruler? 2. Gretchen is putting together a bookcase. It came with diagonal support bars that are to be screwed into the top and bottom on the back of the bookcase. Unfortunately, the instructions were lost and Gretchen does not have the directions or a measuring tool. She has a screwdriver, a marker, and a piece of string. How can Gretchen attach the supports to make certain the bookcase will be a rectangle and the shelves are parallel to the ground?.1 Properties of Squares and Rectangles 751

12 3. Matsuo knows this birdhouse has a rectangular base, but he wonders if it has a square base. a. What does Matsuo already know to conclude the birdhouse has a rectangular base? b. What does Matsuo need to know to conclude the birdhouse has a square base? 4. Consider each LED television shown. x 27 x 30 y 29.4 y 32 a. Determine the dimensions of the 270 LED TV. A TV screen is always measured in inches from corner to corner on a diagonal. 752 Chapter Properties of Quadrilaterals

13 b. Determine the dimensions of the 300 LED TV. c. Compare the viewing area of each size television screen. d. What property of a rectangle would be helpful when locating the center point of the television screen? e. What property of a rectangle would be helpful when determining the perimeter of the television screen?.1 Properties of Squares and Rectangles 753

14 5. Sketch a square. Label the midpoint of each side of the square. a. Determine the polygon formed by connecting the midpoints of each side of a square and justify your conclusion. y x Consider the sketch of your square so your algebraic justifications will include x- and y-intercepts. 754 Chapter Properties of Quadrilaterals

15 b. If the same process was repeated one more time by connecting the midpoints of each side of the polygon determined in part (a), describe the polygon that would result. Be prepared to share your solutions and methods..1 Properties of Squares and Rectangles 755