Question

Find the measure of angle CDE.
A. 50°
B. 65°
C. 115°
D. 130°

Answer 1

There is a theorem that states:
The measure of an exterior angle of a triangle is equal to the sum of the measures of its remote interior angles.
Do you uinderstand the terms "exterior angle," and "remote interior angles"?

Answer 2

yes @mathstudent55!

Answer 3

Then what for this triangle, what equation can you write that relates the measures of three angles?

Answer 4

2x - 15 = x +50
2x - 15+15 = x +50+15
2x = x +65

2x-x = x -x +65
x = 65

Ok we found x but we want angle CDE

CDE = 2x - 15

Plug in back 65

2(65) - 15= 130-15= 115

Answer 5

thank you @Nurali

Answer 6

My pleasure.