1. Bellwork
For Exercises 1 and 2, find the value of x. Give your answer in simplest radical form.
Simplify each expression.

3. Example 1A: Finding Side Lengths in a 45°- 45º- 90º Triangle
Find the value of x. Give your answer in simplest radical form.

4. Example 1B: Finding Side Lengths in a 45º- 45º- 90º Triangle
Find the value of x. Give your answer in simplest radical form.
Rationalize the denominator.

5. Example 1c
Find the value of x. Give your answer in simplest radical form.
x = 20
Simplify.

6. Example 2: Craft Application
Jana is cutting a square of material for a tablecloth. The table’s diagonal is 36 inches. She wants the diagonal of the tablecloth to be an extra 10 inches so it will hang over the edges of the table. What size square should Jana cut to make the tablecloth? Round to the nearest inch.
= 46 inches

7. A 30°-60°-90° triangle is another special right triangle
A 30°-60°-90° triangle is another special right triangle. You can use an equilateral triangle to find a relationship between its side lengths.
Hypotenuse = 2(shorter leg)

8. Example 3A: Finding Side Lengths in a 30º-60º-90º Triangle
Find the values of x and y. Give your answers in simplest radical form.
22 = 2x
Hypotenuse = 2(shorter leg)
11 = x
Divide both sides by 2. 11
Substitute __ for x.

9. Example 3B: Finding Side Lengths in a 30º-60º-90º Triangle
Find the values of x and y. Give your answers in simplest radical form.
Rationalize the denominator.
y = 2x
Hypotenuse = 2(shorter leg).
Simplify.

10. Rationalize the denominator.
Example 3c
Find the values of x and y. Give your answers in simplest radical form.
Rationalize the denominator. 3
x = 2y
Hypotenuse = 2(shorter leg)
Simplify.

11. The height of the triangle is the length of the ________ leg.
Example 4
What if…? A manufacturer wants to make a larger clock with a height of 30 centimeters. What is the length of each side of the frame? Round to the nearest tenth.
Step 1 The equilateral triangle is divided into ____ 30º-60º-90º triangles.
Two, longer
The height of the triangle is the length of the ________ leg.

12. Check It Out! Example 4 Continued
Step 2 Find the length x of the shorter leg.
Rationalize the denominator.
Step 3 Find the length y of the longer leg.
y = 2x
34.6
Hypotenuse = 2(shorter leg)
Simplify.
Each side is approximately _____ cm.

13. Lesson Quiz: Part I
Find the values of the variables. Give your answers in simplest radical form.
x = 10; y = 20

14. Lesson Quiz: Part II
Find the perimeter and area of each figure. Give your answers in simplest radical form.
5. a square with diagonal length 20 cm
6. an equilateral triangle with height 24 in.

15. Applying Special Right Triangles
5-8
Applying Special Right Triangles
Warm Up
Lesson Presentation
Lesson Quiz
Holt McDougal Geometry
Holt Geometry

16. Objectives Justify and apply properties of 45°-45°-90° triangles.

17. A diagonal of a square divides it into two congruent isosceles right triangles. Since the base angles of an isosceles triangle are congruent, the measure of each acute angle is 45°. So another name for an isosceles right triangle is a 45°-45°-90° triangle.
A 45°-45°-90° triangle is one type of special right triangle. You can use the Pythagorean Theorem to find a relationship among the side lengths of a 45°-45°-90° triangle.

18. Check It Out! Example 1b
Find the value of x. Give your answer in simplest radical form.
The triangle is an isosceles right triangle, which is a 45°-45°-90° triangle. The length of the hypotenuse is 16.
Rationalize the denominator.

19. Check It Out! Example 2
What if...? Tessa’s other dog is wearing a square bandana with a side length of 42 cm. What would you expect the circumference of the other dog’s neck to be? Round to the nearest centimeter.
Tessa needs a 45°-45°-90° triangle with a hypotenuse of 42 cm.

20. Check It Out! Example 3a
Find the values of x and y. Give your answers in simplest radical form.
Hypotenuse = 2(shorter leg)
Divide both sides by 2.
y = 27
Substitute for x.

21. Check It Out! Example 3c
Find the values of x and y. Give your answers in simplest radical form.
24 = 2x
Hypotenuse = 2(shorter leg)
12 = x
Divide both sides by 2.
Substitute 12 for x.

22. Example 3c
Find the values of x and y. Give your answers in simplest radical form.
y = 2(5)
y = 10
Simplify.

23. Example 4: Using the 30º-60º-90º Triangle Theorem
An ornamental pin is in the shape of an equilateral triangle. The length of each side is 6 centimeters. Josh will attach the fastener to the back along AB. Will the fastener fit if it is 4 centimeters long?
Step 1 The equilateral triangle is divided into two 30°-60°-90° triangles.
The height of the triangle is the length of the longer leg.