IM 8 Ch Does It Always Work. Common Core Standard: Is the triangle a right triangle? Who is Pythagoras? CPM Materials modified by Mr.

Transcription

1 Common Core Standard: 8.G.6 Is the triangle a right triangle? Who is Pythagoras? CPM Materials modified by Mr. Deyo

2 Title: IM8 Ch Does It Always Work? Date: Learning Target By the end of the period, I will explain a proof of the Pythagorean Theorem and its converse. I will demonstrate this by completing Four Square notes and by solving problems in a pair/group activity.

3 Home Work: Sec Desc. Date Due Review & Preview 4 Problems 9 149, 9 150, 9 151, 9 154

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5 Vocabulary 1) right triangle 2) leg(s) (a & b) 3) hypotenuse (c) 4) Pythagorean Theorem a 2 + b 2 = c 2

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7 9.2.7 Does It Always Work? You have seen that you can find the missing side of a right triangle using the Pythagorean Theorem. To show that it is always true, no matter how long the sides are, it must be proven. There are over 100 different ways to prove this important relationship. Today you will look at two ways to prove the Pythagorean Theorem. As you may remember, the Pythagorean Theorem states that in a right triangle with sides a and b, and hypotenuse c, a 2 + b 2 = c 2. %20RP.pdf Obtain the Lesson 9.2.7A Resource Page from your teacher. For additional support, watch Pythagorean Proof Video b c a a c b

8 9 145a,b) Start by cutting out four copies of the right triangle with legs labeled a, b, and hypotenuse labeled c units. a) First, arrange the triangles to look like the diagram at right. Draw this diagram on your paper. Explain why the area of the unshaded region is c 2. b) Will moving the triangles within the bold outer square change the total unshaded square? %20RP.pdf b c a a c b

9 9 145) c) Move the shaded triangles to match the diagram at right. In this arrangement, tell why the total area that is unshaded is a 2 + b 2. %20RP.pdf d) Write an equation that relates the unshaded region in part (a) to the unshaded region in part (b). b c a a c b

10 Here is another proof of the Pythagorean Theorem for you to try. Obtain the Lesson 9.2.7B Resource Page from your teacher. a) Start with two squares as shown here. What is the total area? c b a c a b) Use a ruler or another piece of paper to place a mark of length b on the bottom left side of the larger square. Then draw the dotted lines as shown in the diagram at right to create two right triangles. How do you know that the legs of both triangles are legs a and b? Label each hypotenuse c. c) Cut out the shaded triangles shown in the diagram at right. Then work with your team to determine how to arrange the shaded triangles and the unshaded portion of the original figure to create a square. What is the area of the square? How do you know? b d) How does what you have done in this problem prove the Pythagorean Theorem?

11 9.2.1A # %20RP.pdf 147b)

12 The converse of a theorem reverses the evidence and the conclusion. The Pythagorean Theorem states that in a right triangle with legs of a and b, and hypotenuse c, that a 2 + b 2 = c 2. a) State the converse of the Pythagorean Theorem. b) Look back at your work from problem What can you conclude about a triangle if a 2 + b 2 = c 2? c) Why is this not a proof of the converse of the Pythagorean Theorem?

13 Graph the points A( 2, 2) and B(1, 2). Then find the distance between them by creating a right triangle (like a slope triangle) and computing the length of the hypotenuse.

14 Use a graph to find the distance between the points C( 4, 1) and D(4,1). hom chapter/ch9/lesson/9.2.7/problem/

15 Jack has a tree in his backyard that he wants to cut down to ground level. He needs to know how tall the tree is, because when he cuts it, it will fall toward his fence. Jack measured the tree s shadow, and it measured 20 feet long. At the same time, Jack s shadow was 12 feet long. Jack is 5 feet tall. chapter/ch9 Tree Jack a) How tall is the tree? b) Will the tree hit the fence if the fence is 9 feet away?

16 Examine the diagrams below. What is the geometric relationship between the labeled angles? What is the relationship of their measures? After you determine the relationship of their measures, use the relationship to write an equation and solve for x. a) b) chapter/ch9/lesson/9.2.

17 On graph paper, graph the system of equations below. Graph y = 2 x y = 2 x What's the solution of the system? (, ) chapter/ch9 If there is no solution, explain why not.

18 A principal made the histogram at right to analyze how many years teachers had been teaching at her school. homework/homework/category/cc/textbook/c chapter/ch9/lesson/9.2.7/problem/9 153 a) How many teachers work at her school? b) If the principal randomly chose one teacher to represent the school at a conference, what is the probability that the teacher would have been teaching at the school for more than 10 years? Write the probability in two different ways. c) What is the probability that a teacher on the staff has been there for fewer than 5 years?

19 9 154a,b. Simplify each expression. a) b) ( 1) 3 chapter/ch9/lesson/9.2.7/p

20 9 154c,d. Simplify each expression. c) d*) ( ) 9 5 ( 10) 3 chapter/ch9/lesson/9.2.7/p