Shapes SE Inv 3 V15 1. Designing Triangles and Quadrilaterals. Bridges, towers, and other structures contain many triangles in their design.

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1 Shapes SE Inv 3 V15 1 Investigation 3 Designing Triangles and Quadrilaterals Your work on problems of Investigation 2 revealed properties of polygons that make them useful in natural objects like the honeycombs made by bees. In this investigation you will discover properties of polygons that make them useful in buildings, mechanical devices, and crafts. To explore the connections between shapes and their uses in construction, it will be helpful to actually build some polygons using polystrips and fasteners like these: These tools will allow you to build and study polygons with various combinations of side lengths and angles. 3.1 Building Triangles Bridges, towers, and other structures contain many triangles in their design. What properties of these simple polygons could make them so valuable in construction?

2 2 Shapes SE Inv 3 Draft 15 Problem 3.1 The best way to discover what is so special about triangles in construction is to build several models and study their reaction to pressure. A. Make and study several test triangles using the steps below. Sketch and label your results. Step 1 Pick three numbers between 2 and 20 to be side lengths of a polystrip triangle. Step 2 Try to make a triangle with the chosen side lengths. If you can build one such triangle, try to build a different triangle with the same side lengths. Then repeat Steps 1 and 2 to make and study several other triangles. Record your results in a table with headings like this: Side Lengths Triangle Possible? Sketch Different Shape? Be sure to list some sets of side lengths with which you could make a triangle and some sets of side lengths with which you could not make a triangle. B. Study the results of your experimentation with different side length possibilities. 1. What pattern do you see that explains why some sets of numbers make a triangle and some do not? 2. In what cases can you make more than one triangle from a given set of side lengths? 3. Use your discoveries to find three other side lengths that will make a triangle. Then find three other side lengths that will not make a triangle. 3.2 Design Challenge II: Drawing Triangles The drawing here shows a triangle with measures of all angles and sides. A 3cm 74 o 3.6cm B 60 o 4 cm 46 o C If you wanted to text a friend giving directions for drawing an exact copy of the figures, what is the shortest message that would do the job?

3 Shapes SE Inv 3 V15 3 Problem 3.2 To find an answer to the challenge of describing triangles in only a few words, it might help to work through the parts of this problem. A. Which of these short messages give enough data to draw a triangle that has the same size and shape as ΔABC shown above? 1. Side-Angle-Side Segment BC = 4 cm B = 60 BA = 3 cm 3. Side-Side-Angle AB = 3 cm ; BC = 4 cm ; C = Angle-Angle-Side B = 50 C = 40 ; AC = 4 cm. 2. Angle-Side-Angle B = 60 BC = 4 cm; C = 46 ; 4. Angle-Angle-Angle B = 60 A = 74 C = 46 ; B. Write the shortest possible messages that tell how to draw triangles that will have the same size and shape as those shown here: L A J K C B R H G T S F

4 4 Shapes SE Inv 3 Draft 15 C. What minimum information about a triangle will allow you to draw exactly one triangle? 3.3 Building Quadrilaterals Quadrilaterals, especially rectangles, appear throughout every buildings in which we live, work, and go to school. You see them on the outside in the outlines of bricks, the frames of windows, and the outlines of large buildings. On the inside, almost every building stands up because of a rectangular frame of studs and beams. But rectangles have physical properties that are very different from triangles. Do quadrilaterals have the same relationship among its sides as triangles? What properties do quadrilaterals have that make them useful? Problem 3.3 As with your study of triangle properties, it will help you to understand the facts of life with quadrilaterals if you use polystrips to build and test some samples. A. Build polystrip quadrilaterals with each of the following sets of numbers as side lengths. If you succeed in building one quadrilateral with a set of side lengths, try to build two or more different figures using the same set of side lengths. 1. Side lengths 6, 10, 15, Side lengths 3, 5, 10, Side lengths 8, 8, 10, Side lengths 12, 20, 6, 9 Sketch and label results to share with your classmates. Record any observations you make. B. Choose your own sets of four numbers and try to build quadrilaterals with those numbers as side lengths. Combine observations from your testing and the examples in Part A to answer these questions:

5 Shapes SE Inv 3 V Is it possible to make a quadrilateral using any four side lengths? If not, how can you tell when you can make a quadrilateral from four side lengths? 2. Can you make two or more different quadrilaterals from the same four side lengths? 3. What combinations of side lengths are needed to build rectangles? Squares? Parallelograms? C. Now use several of your polystrip figures to study the reaction of triangles and quadrilaterals to stress. 1. What happens when you hold one of your triangles upright and push down on a vertex as the weight of a car or train would act on a bridge? Push Downward Push Downward 2. What happens when you hold one of your quadrilaterals upright and push down on a side or vertex? 3. How do the results of the polystrip constructions and stress tests explain the frequent use of triangles in building structures like bridges and towers? D. Use another polystrip to add a diagonal connecting a pair of opposite vertices in one or more of your test quadrilaterals. Then repeat the stress test by pressing on the sides or corners of the quadrilateral. Why do you think there is a different response to pressure when a diagonal brace is added to a quadrilateral?

6 6 Shapes SE Inv 3 Draft 15 E. Describe the similarities and differences between what you learned about building triangles in Problem 3.1 and building quadrilaterals in this problem. How do the differences explain the frequent use of triangles in building structures. Did You Know? Mechanical engineers use the fact that quadrilaterals are not rigid figures to design linkages. Here is an example of a quadrilateral linkage made from polystrips. One of the sides is fixed. It is the frame. The two sides attached to the frame are the cranks. One of the cranks is the driver and the other the follower. The fourth side is called the coupler. Quadrilateral linkages are used in windshield wipers, automobile jacks, reclining lawn chairs, and handcars.

7 Shapes SE Inv 3 V15 7 frame crank crank coupler In 1883, the German mathematician Franz Grashof suggested an interesting principle for quadrilateral linkages: If the sum of the lengths of the shortest and longest sides is less than or equal to the sum of the lengths of the remaining two sides, then the shortest side can rotate Parallel Lines and Transversals If you were asked to build a quadrilateral with side lengths 3, 8, 3, and 8 you would probably guess that the expected figure is a 3 8 rectangle. But your experiments in Problem 3.2 showed that if you push on any of the vertices of a polystrip rectangle, it loses its square-corner shape. The one thing that doesn t change about the polystrip figure is the relationship of opposite sides they remain equal in length and parallel to each other.

8 8 Shapes SE Inv 3 Draft 15 Parallel lines are lines in a plane that never meet. Like the tracks of a railroad, rows of crops in a field, or the lines on notebook paper, they remain the same distance apart and never meet, even if extended forever in both directions. A parallelogram is a quadrilateral in which pairs of opposite sides are parallel. The shape of a parallelogram is largely set by the angles at which those pairs of sides meet. A parallelogram with four right angles is a rectangle. Problem 3.4 A. There are nine parallelograms among the figures in the Shapes Set of Problem What pattern seems to relate measures of opposite angles in any parallelogram? 2. What pattern seems to relate measures of consecutive angles in any parallelogram? 3. If your conjectures in Parts 1 and 2 are correct, what are the measures of the angles in parallelograms ABCD and JKLM shown below? M C D A L o 60 o 135 B J K B. If your conjecture from Part A is true, you can find the measures of all labeled angles in this diagram. Be prepared to justify each answer.

9 Shapes SE Inv 3 V15 9 m n l o k h j i a 150 o g f b c d e C. When a line intersects two other lines, the intersecting line is called a transversal. 1. Based on your work in Parts A and B, what do you think you can say about measures of the eight angles formed when a transversal intersects two parallel lines as in the diagram below? 2. If the measure of angle e is 80, what are the measures of the other labeled angles? t a d b c L 1 e h f g L 2 D. You probably noticed that when two lines intersect, as when a transversal cuts one of two parallels, four angles are formed. The opposite pairs of angles are called vertical angles. For example, in the figure of Part C, angles e and g are vertical angles. 1. Name the other pairs of vertical angles in the figure of Part C. 2. Name the pairs of supplementary angles in that figure. 3. What is true about the measures of any vertical angle pair? Explain how you know. E. Use what you know about supplementary and vertical angles to find the value of x and the size of each angle in this figure.

10 10 Shapes SE Inv 3 Draft Design Challenge III: The Quadrilateral Game Special properties of triangles and quadrilaterals make them useful in design of buildings and mechanical objects. They also play an important role in design of craft objects like the quilts shown here. In both the overall design and in many of the pieces that make up the design, there is a balance that is pleasing to the eye. The quilts show two common forms of symmetry: Reflection Symmetry Rotation Symmetry A shape with reflection symmetry has halves that are mirror images of each other. If you fold the figure along its line of symmetry, the two halves of the shape will match exactly. If you hold a mirror along the line of symmetry, A shape with rotation symmetry can be turned about a center point through some angle between 0 and 360 degrees without changing the appearance of the shape. If you close your eyes while the figure above is rotated 120º or

11 Shapes SE Inv 3 V15 11 the image in the mirror will match exactly the half of the figure behind the mirror! 240º and then open them again, you won t notice that anything had changed! Spotting symmetries in polygons is the first step in using those figures to make art and craft designs. What kind of symmetries do the triangles in the shape set have? What kind of symmetries do the quadrilaterals in the shape set have? Look at the remaining polygons in the Shape Set and describe any symmetries that you find. Look for objects in your classroom or in nature that have symmetries. What kind of symmetries do they have? The final problem of this unit involves a game. The Quadrilateral Game challenges you to use all that you know about polygons including symmetry. The game is played by two teams. To play, you need two number cubes, a game grid, a geoboard, and a rubber band. Quadrilateral Game Rules Near the center of the geoboard, put the rubber band around a square measuring one unit on each side. Team A rolls the number cubes one at a time to locate an entry in the game grid on the next page. The first number locates the row and the second number locates the column. Team A reads the description in that location. Team A then looks at the quadrilateral already on the game board, and forms a new quadrilateral to match the description. They move as few corners of the already existing quadrilateral as possible. Team A receives one point for each corner moved. Next, Team B rolls the number cubes and locates the corresponding description on the grid. They make a quadrilateral fitting the new description by moving as few corners of the existing quadrilateral as possible. Team B receives one point for each corner moved. Play continues until each team has had five turns. The team with the lowest score at the end is the winner.

12 12 Shapes SE Inv 3 Draft 15 Problem 3.5 Play the Quadrilateral Game and keep a record of interesting strategies and difficult situations. A. When did you receive 0 points during a turn? Why did you not need to move any corners on those turns? B. Write two new descriptions of quadrilaterals that you could use in the game grid. C. Write a set of cards with descriptions about triangles that could be used in a Triangle Game.

13 Shapes SE Inv 3 V15 13 Follow these directions for Exercises 1 4. If possible, build a triangle with the given set of side lengths. Sketch your triangle. Tell whether your triangle is the only one that is possible. Explain. If a triangle is not possible, explain why. 1. Side lengths of 5, 5, and 3 2. Side lengths of 8, 8, and 8 3. Side lengths of 7, 8, and Side lengths of 5, 6, and Which sets of side lengths from Exercises 1 4 can make each of the following shapes? a. an equilateral triangle (a triangle in which all three sides are equal length) b. an isosceles triangle (a triangle in which two sides are equal length) c. a scalene triangle (a triangle in which no two sides are equal length) d. a triangle with at least two angles of the same measure For Exercises 6 and 7, draw the polygons described to help you answer the questions. 6. What do you think must be true of the side lengths in order to build a triangle with three angles measuring 60? What kind of triangle is this? 7. What do you think must be true of the side lengths in order to build a triangle with only two angles the same size? What kind of triangle is this? 8. Giraldo and Maria are building a tent. They have two 3-foot poles. In addition, they have a 5-foot pole, a 6-foot pole, and a 7-foot pole. They want to make a triangular-shaped doorframe for the tent using both 3-foot poles and one of the other poles. Which of the other poles could be used to form the base of the door?

14 14 Shapes SE Inv 3 Draft Which of these descriptions of a triangle ABC give directions that can be followed to draw exactly one shape? a. AB = 2.5 in; AC = 1 in; B = 40 b. AB = 2.5 in; AC = 1 in; A = 40 c. AB = 2.5 in; ; B = 60 ; and A = 40 d. AB = 2.5 in; ; B = 60 ; and A = 130 Follow these directions for Exercises If possible, build a quadrilateral with the given set of side lengths. Sketch your quadrilateral. Tell whether your quadrilateral is the only one that is possible. Explain. If a quadrilateral is not possible, explain why. 10. Side lengths of 5, 5, 8, and Side lengths of 5, 5, 6, and Side lengths of 8, 8, 8, and Side lengths of 4, 3, 5, and Which set(s) of side lengths from Exercises can make each of the following shapes? a. a square b. a quadrilateral with all angles the same size c. a parallelogram

15 Shapes SE Inv 3 V15 15 d. a quadrilateral that is not a parallelogram 15. A quadrilateral with four equal sides is called a rhombus. Which set(s) of side lengths from Exercises can make a rhombus? 16. A quadrilateral with just one pair of parallel sides is called a trapezoid. Which set(s) of side lengths from Exercises 9 12 can make a trapezoid? 17. In the diagram below, line T is a transversal to parallel lines L 1 and L 2. a. Find the degree measures of angles labeled a g. b. Name the pairs of opposite or vertical angles in the figure. b a c 35 o L 1 g T d f e L Which of these shapes have reflection and/or rotation symmetry? Multiple Choice For Questions 19 22, choose the symmetry or symmetries of each shape. 19. Rhombus (four equal sides) A. rotation B. reflection C. both A and B D. none 20. Regular pentagon F. rotation G. reflection H. both F and G J. none 21. Square A. rotation B. reflection C. both A and B D. none 22. A parallelogram that is not a rhombus or a rectangle

16 16 Shapes SE Inv 3 Draft 15 F. rotation G. reflection H. both F and G J. none For Exercises 23 and 24, draw the polygons described to help you answer the questions. 23. What must be true of the side lengths of a polygon to build a square? 24. What must be true of the side lengths of a polygon to build a rectangle that is not a square? 25. Li Mei builds a quadrilateral with sides that are each five inches long. To help stabilize the quadrilateral, she wants to insert a ten-inch diagonal. Will that work? Explain. 26. You are playing the Quadrilateral Game. The shape currently on the geoboard is a square. Your team rolls the number cubes and gets the description A parallelogram that is not a rectangle. What is the minimum number of vertices your team needs to move to form a shape meeting this description? 27. Suppose you are playing the Quadrilateral Game. The shape currently on the geoboard is a parallelogram but not a rectangle. Your team rolls the number cubes and gets the description A quadrilateral with two obtuse angles. What is the minimum number of vertices your team needs to move to create a shape meeting this description? Connections 28. Multiple Choice: Which one of the following shaded regions is not a representation of 4 12? 29. Compare the three quadrilaterals shown below. a. How are all three quadrilaterals alike? b. How does each quadrilateral differ from the other two?

17 Shapes SE Inv 3 V Find the measure of each numbered angle in this figure showing a parallelogram and two exterior angles Think about your polystrip experiments with triangles and quadrilaterals. What explanations can you now give for the common use of triangular shapes in structures like bridges and towers for transmitting radio and television signals? o 32. Below is a rug design from the Southwest United States. a. Name some of the polygons in the rug. b. Describe the symmetries of the design.

18 18 Shapes SE Inv 3 Draft Here are three state flags. a. Describe the lines of symmetry in each whole flag. b. Do any of the shapes or designs within the flags have rotational symmetry? If so, which ones? c. Design your own flag. Your flag should have at least one line of symmetry. Your flag should also include three shapes that have rotational symmetry. List the shapes in your flag that have rotational symmetry. For Exercises 34-35, use these quilt patterns. Pattern A Pattern B

19 Shapes SE Inv 3 V Name some of the polygons in each quilt pattern. 35. Describe the symmetries of each quilt pattern. 36. Half of the figure below is hidden. The vertical line is a line of symmetry for the complete figure. Copy the part of the figure shown. Then draw the missing half. 37. Multiple Choice. A triangle has a base of 4 and an area of 72. Which of the following is true. A. These properties do not make a triangle. B. These properties make a unique triangle. C. There are at least two different triangles with these properties. D. The height of the triangle is Multiple Choice. Which of the following could NOT be the dimensions of a parallelogram with an area of 18. A. base = 18 height = 1 B. base = 9 height = 3 C. base = 6 height = 3 D. base = 2 height = 9 Extensions 39. In the triangle ABC, a line has been drawn through vertex A, parallel to side BC.

20 20 Shapes SE Inv 3 Draft 15 1 A 2 3 B 6 5 C a. What is the sum of the measures of angles 1, 2, and 3? b. Explain why angle 1 has the same measure as angle 6 and why angle 3 has the same measure as angle 5. c. How do the results of parts (a) and (b) to show that the angle sum of a triangle is 180? 40. Explore properties of pentagons with experiments using polystrips or sketches. Use your results to answer the following questions. a. If you choose five numbers as side lengths, can you always build a pentagon? Explain. b. Can you make two or more different pentagons from the same set of side lengths? c. Can you find side lengths for a pentagon that will tile a surface? Explain. 41. Refer to the Did You Know? after Problem 3.3. a. Make a model that illustrates Grashof s principle using polystrips. Describe the motion of your model. b. How can your model be used to make a stirring mechanism? A windshield wiper? 42. Build the figure shown next from polystrips. Note that the vertical sides are all the same length, the distance from B to C equals the distance from E to D, and the distance from B to C is twice the distance from A to B. a. Experiment with holding various strips fixed (one at a time) and moving the other strips. In each case, tell which strip you held fixed, and describe the motion of the other strips. b. Fix a strip between points F and B and then try to move strip CD. What happens? Explain why this occurs.

21 Shapes SE Inv 3 V The drawing below shows a quadrilateral with measures of all angles and sides. If you wanted to text a friend giving directions for drawing an exact copy of the figures, what are some short messages that would do the job? B A 110 o 3.7cm 3cm 60 o 4 cm 75 o D 2.3cm 115 o C a. Which of the following short messages give enough data to guide drawing of a quadrilateral that has the same size and shape as ABCD shown above? i. AB = 3 cm ; BC = 4 cm; CD = 2.3 cm. ii. AB = 3 cm ; B = 60 ; BC = 4 cm; C = 115 ; A = 110. iii. AB = 3 cm, B = 60 ; BC = 4 cm; C = 115 ; CD = 2.3 cm b. Write shortest possible messages that tell how to draw quadrilaterals that will have the same size and shape as those shown here: i. ii.

22 22 Shapes SE Inv 3 Draft 15 D C H G E F A B iii. iv. S M L P J K Q R c. What is the minimum information about a quadrilateral that will allow you to draw an exact copy? For Exercises 44-48, one diagonal of each quadrilateral has been drawn. Complete parts (a) and (b) for each quadrilateral. a. Is the given diagonal a line of symmetry? Why or why not? b. Does the figure have any other lines of symmetry? If so, copy the figure and sketch the symmetry lines.

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24 24 Shapes SE Inv 3 Draft 15 Mathematical Reflections 3 In this investigation, you experimented with building polygons by choosing lengths for the sides and then connecting those sides to make a shape. You also studied ways to describe triangles and quadrilaterals accurately and efficiently. The following questions will help you summarize what you have learned. Think about your answers to the questions. Discuss your ideas with other students and your teacher. Then write a summary of findings in your notebook. 1. What information about combinations of angles sizes and side lengths will provide enough information to copy a given triangle exactly? A quadrilateral? 2. Why are triangles so useful in building structures? What are the problems with quadrilaterals in such structures? 3. If two parallel lines are intersected by a transversal, which pairs of angles will have the same measure? 4. What does it mean to say a figure has symmetry? Provide examples with your explanation. Unit Project: What discoveries in the problems of this investigation seem worthy of inclusion in a unit project report, poster, or presentation? Mathematical Practices Reflections Every day, as you worked on the problems in this investigation, you used prior knowledge to make sense of the problem and applied the Mathematical Practices used by successful mathematicians. For example, you and your classmates discussed strategies, observed patterns and relationships, made conjectures, validated conjectures, generalized, and extended patterns. Think back over your work and identify times when you used these ways of thinking about mathematical problems and questions. Students in CMP classrooms have used some of these practices as follows: MP5. Use appropriate tools strategically. We noticed the usefulness of polystrips to help us determine the side lengths of triangles in Problem 3.1. We chose three different numbers and used our polystrips to see if they created a triangle. It was important to understand how the polystrips worked so we could decide if we could make more than one triangle with the same side lengths. MP6. Attend to precision.

25 Shapes SE Inv 3 V15 25 In Problem 3.2, we had to determine the shortest possible message we could tell our friend to enable them to draw a replica of our triangle. We noticed there were three pieces of information that needed to be included in our message, but it was not just any three pieces, there were specific types of information that needed to be included. We also had to write clear descriptions so our friend was able to duplicate the correct triangle. What other practices are illustrated by this example? Describe one other instance of the Mathematical Practices that you and your classmates used in this investigation to solve problems.