1. Inside angles theorem

2. All angles in a triangle sum up to 180˚

3. Examples:

4. Find the value for the missing angle:

5. Exterior angle theorem

7. Examples:
40⁰
90⁰
50⁰
140⁰
= 50⁰ + 90⁰
90⁰
= 50⁰ + 40⁰

8. Examples: 120⁰ = 35⁰ + 85⁰ 85⁰ 35⁰ 60⁰ 145⁰ = 85⁰ + 60⁰ 95⁰
= 35⁰ + 60⁰

9. Find the value for the indicated angle

10. Isosceles triangle theorem

11. If two sides of a triangle are congruent, then the angles opposite to those sides are congruent.

12. Examples

13. Find the value OF X:
2x+5
65˚
83˚ X˚

15. Find the value of x:
103 m X
2X-10 90

16. For help with exterior angle theorem, copy the link and watch:
For help with the sum of the interior angles of a triangle, copy the link and watch: