1. Complete “You Try” section p.11 in your workbook!

2. Homework Answers

4. Discovering 30-60-90 Special Triangles

5. We begin with an equilateral triangle with 1 unit on each side
We begin with an equilateral triangle with 1 unit on each side. This is shown below.
Find the measurement of all the angles and the lengths of each side. Construct an altitude from the top vertex to the base in the above square. The diagonal creates two smaller triangles in your above triangle. Find the angle measures of the angles in the two triangles and the new length of the base of the two triangles. Using the Pythagorean Theorem, find the length of the altitude (or the hypotenuse of the right angle triangle). KEEP IN RADICAL FORM.

6. We begin with an equilateral triangle with 2 unit on each side
We begin with an equilateral triangle with 2 unit on each side. This is shown below.
Find the measurement of all the angles and the lengths of each side. Construct an altitude from the top vertex to the base in the above square. The diagonal creates two smaller triangles in your above triangle. Find the angle measures of the angles in the two triangles and the new length of the base of the two triangles. Using the Pythagorean Theorem, find the length of the altitude (or the hypotenuse of the right angle triangle). KEEP IN RADICAL FORM.

7. We begin with an equilateral triangle with 3 unit on each side
We begin with an equilateral triangle with 3 unit on each side. This is shown below.
Find the measurement of all the angles and the lengths of each side. Construct an altitude from the top vertex to the base in the above square. The diagonal creates two smaller triangles in your above triangle. Find the angle measures of the angles in the two triangles and the new length of the base of the two triangles. Using the Pythagorean Theorem, find the length of the altitude (or the hypotenuse of the right angle triangle). KEEP IN RADICAL FORM.

8. Equilateral with ____ Units Side length of Hypotenuse
Side length of Base
Side Length of Altitude 4 8 10 12 16

9. Do you see a pattern. Explain
Do you see a pattern? Explain. Conclusion: Given an equilateral triangle with “x” unit on each side, what would be the lengths of the sides, and the lengths of the altitude?

10. 8.3: Special Right Triangles

11. Equilateral Triangle Relationship
Equilateral Triangle Relationship
A 30° – 60° – 90° triangle is another special right triangle. You can use an equilateral triangle to find this relationship. When the altitude is drawn from any vertex of an equilateral triangle, two congruent 30° – 60° – 90° triangles are formed. In the figure shown, ∆ 𝐴𝐵𝐷≅∆𝐶𝐵𝐷, so 𝐴𝐷 ≅ 𝐶𝐷. If CD = x, then AC = 2x. This leads to the next theorem.

12. *ℎ𝑦𝑝𝑜𝑡𝑒𝑛𝑢𝑠𝑒=𝑠ℎ𝑜𝑟𝑡 𝑙𝑒𝑔∙2 *𝑙𝑜𝑛𝑔𝑒𝑟 𝑙𝑒𝑔=𝑠ℎ𝑜𝑟𝑡 𝑙𝑒𝑔 ∙ 3
30˚-60˚-90˚
Triangle Theorem
In a 30˚-60˚-90˚ Triangle, the hypotenuse 𝒉 is 2 times the length of the shorter leg 𝒔 and the length of the longer leg 𝒍 is 3 times the length of the shorter leg.
*ℎ𝑦𝑝𝑜𝑡𝑒𝑛𝑢𝑠𝑒=𝑠ℎ𝑜𝑟𝑡 𝑙𝑒𝑔∙2
*𝑙𝑜𝑛𝑔𝑒𝑟 𝑙𝑒𝑔=𝑠ℎ𝑜𝑟𝑡 𝑙𝑒𝑔 ∙ 3
 *ℎ=𝑠∙2
 *𝑙=𝑠 3

13. Example 4: Find x and y. a)

14. Example 4: Find x and y. b)

15. Example 4: Find x and y. c)

16. Example 5:
A quilt has the design shown in the figure, in which a square is divided into 8 isosceles right triangles. If the length of one side of the square is 3 inches, what are the dimensions of each triangle?

17. Example 6:
Shaina designed 2 identical bookends according to the diagram below. Use special triangles to find the height of the bookends.

18. Example 7.
An equilateral triangle has a side length of 10 inches. Find the length of the triangles altitude.

19. Example 8.
The altitude of an equilateral triangle is 18 inches. Find the length of a side.

20. Summary!
Find all the missing side lengths. Leave answers in simplified radical form.

21. Summary!
Find all the missing side lengths. Leave answers in simplified radical form.

22. Homework Answers: WB p.30-31
𝑥= ) x = 3 3) 𝑥=4 2
4) 𝑥= ) 𝑥= ) 𝑥=14 2
7) x = 1, y = ) 𝑥=8 3 , 𝑦=16
9) 𝑥=5.5,𝑦= ) 𝑥=24 3
11) 𝑥=30 3

23. Exit Slip
Find the values of x and y.