Question

Find the measure of angles 1–12 in the complex figure. Explain how you found each angle measure.

•line a || line b
•line c || line d
•segment EG || line e

Answer 1

I'll start with the triangle figure.
Interior angles of a triangle is equal to 180°. The given triangle is an Isosceles triangle. It has 2 equal sides and 2 equal angles.

#7 is 69° because its vertical angle is 69°. Vertical angles are equal.
#8 is 111°. As I said, isosceles triangle has 2 equal angles. The angle that is beside #8 is 69°, equal to #7. So, 180° - 69° = 111°
Interior angles are already given except for #4. So, 180° - 69° - 69° = 42°
#3 is computed by 180° - 42° - 69° = 69°

#9 = 116° ; alternate interior angles are equal.
#10 = 180° - 116° = 64°

The last triangle looks like an equilateral triangle. It means that its sides and angles are equal.

360° / 6 = 60°
#1, #2, #5, and #6 = 60° each
#11 = 60° - equilateral triangle, all interior angles are equal.
#12 = 30°; 180° - 90° - 60° = 30°