### Home > GC > Chapter 12 > Lesson 12.2.3 > Problem 12-77

12-77.

Find the area of the shaded region of the regular pentagon at right. Show all work.

Label the shaded region as

The measure of each angle in a pentagon is equal to

Therefore, the measure of

Divide .

Solve for the length of AD:

Once you know the length of AD, use the formula (1/2)(Base)(Height) to find the area of the shaded triangle.