1. Triangles
Teacher Twins©2014

2. Find the angle measures.
Warm Up
Find the angle measures.
115⁰
65⁰
65⁰
115⁰
115⁰
65⁰
65⁰
115⁰

3. Triangles

4. Triangle Review ________triangles have three acute angles.
________triangles have one obtuse angle.
________triangles have one right angle.
Acute
Obtuse
Right

5. Triangle Review __________ triangles have no congruent sides. Scalene
__________ triangles have at least two congruent sides. Base angles are congruent.
__________ triangles have three congruent sides.
Scalene
Isosceles
Equilateral

6. Triangles and Angles
65⁰ + 55⁰ + 60⁰ = 180⁰
65⁰
55⁰
60⁰

7. Exterior Angle of a Triangle
125⁰
55⁰
Exterior angles
Exterior angles
120⁰
115⁰
65⁰
60⁰
Interior angles

8. Notice that the
interior angle + exterior angle = 180⁰

9. Practice Find x in the right triangle.
39⁰
51⁰
66⁰
2. Find x in the isosceles triangle.
57⁰
57⁰ x x

10. 3. Find the exterior angle.
132⁰ ?
48⁰

11. Closure Find x. 3x + 9 = 180 - 9 = - 9 3x = 171 3 3 x x = 57 x + 5
- 9 =
3x = 171 x
x = 57
x + 5
x + 4