1. Secondary Math 2 8.1 – Triangle Basics
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8.1 – Triangle Basics

2. Warm-UP: with your neighbor/group
Which does not belong? Why?

3. Warm-UP (Part 2) What is the sum of m<1, +m<2 + m<3?
If m<4 = 65˚ and m<5 = 50˚, what is m<2? 1 3 2 4 5

4. What you will learn I will be able to classify triangles.
I will be able to solve for any missing angle.
I will be able to find the area for any triangle.

5. Classification - Sides

6. Classification - Angles

7. Classification – Practice (be specific)

8. The sum of the measures of the interior angles of a triangle is 180˚
Triangle Sum Theorem
The sum of the measures of the interior angles of a triangle is 180˚
The sum of all the angles equals 180˚
(solve for a missing angle)
𝒎<𝟏+𝒎<𝟐+𝒎<𝟑=𝟏𝟖𝟎°

9. Triangle Sum Theorem EXAMPLE
90º
50º
40º

10. PRACTICE!!!!
Solve for x.
70º x
78º
30º x

11. More Practice
#7. Solve for x
7x- 6
𝟖𝟎°
50°

12. Word Problems
The ladder is leaning on the ground at a 75˚ angle. At what angle is the top of the ladder touching the building?

13. EQUILATERAL TRIANGLE
Triangle where ALL 3 sides are congruent
Equilateral triangles are also equiangular (all angles are the same)

14. ISOSCELES TRIANGLES Triangle where 2 sides are congruent
𝐴𝐵 ≅ 𝐶𝐵
Also the two angles opposite the sides are congruent. (<𝐴≅<𝐶)

15. Corollary to Triangle Sum Theorem
*Corollary = statement that readily follows from a theorem (doesn’t need proof, it’s like a natural statement)
The acute angles of a right triangle are complementary.
𝒎<𝑨+𝒎<𝑩=𝟗𝟎°

16. The diagram shows a cross-legged stool
The diagram shows a cross-legged stool. Calculate the angles marked by letters.

17. Calculate the angles marked by letters.

18. Area of a Triangle
𝐴= 𝑏∗ℎ 2

19. AREA PRACTICE