1. -QUIZ
-WARM UP 4.2 -Khan Academy

2. ESSENTIAL QUESTION
How you calculate angle measures in Triangles?

3. Triangle Sum Theorem Theorem 4.2
The sum of the measures of the angles of a triangle is 180

4. Given mA = 43° and mB = 85°, find mC.
Example 1
Find an Angle Measure
Given mA = 43° and mB = 85°, find mC.
SOLUTION
ANSWER
C has a measure of 52°.
Check your solution by substituting 52° for mC. 43° + 85° + 52° = 180° 4

5. ∆ABC and ∆ABD are right triangles. Suppose mABD = 35°.
Example 2
Find Angle Measures
∆ABC and ∆ABD are right triangles.
Suppose mABD = 35°.
Find mDAB. a. b.
Find mBCD.
SOLUTION
mDAB + mABD = 90° a.
mDAB + 35° – 35° = 90° – 35°
mDAB = 55°
mDAB + mBCD = 90° b.
55° + mBCD = 90°
mBCD = 35° 5

6. Checkpoint 1. Find mA. ANSWER 65° 2. Find mB. ANSWER 75° 3.
Find an Angle Measure
Find mA. 1.
ANSWER
65°
Find mB. 2.
ANSWER
75°
Find mC. 3.
ANSWER
50°

7. Exterior Angle Theorem Theorem 4.2
The measure of an exterior angle of a triangle is equal to the sum of the measures of the two nonadjacent interior angles.

8. Given mA = 58° and mC = 72°, find m1.
Example
Find an Angle Measure
Given mA = 58° and mC = 72°, find m1.
SOLUTION
m1 = mA + mC
= 58° + 72°
= 130°
ANSWER
1 has a measure of 130°. 8

9. Checkpoint 4. Find m2. ANSWER 120° 5. Find m3. ANSWER 155°
Find an Angle Measure
Find m2. 4.
ANSWER
120°
Find m3. 5.
ANSWER
155°

10. REVIEW Classify the triangle by its angles and by its sides. 1. ANSWER
acute, isosceles 2.
ANSWER
obtuse, isosceles

11. 3.
Identify which side is opposite each angle.
ANSWER
BC is opposite A; AB is opposite C; AC is opposite B 4.
Brittani built a garden bed frame by nailing together three equal lengths of wood to form a triangle. What type of triangle did she create?
ANSWER
equilateral or equiangular

12. Hw Worksheet 4.2A