### Home > A2C > Chapter 9 > Lesson 9.3.2 > Problem 9-155

9-155.

For each equation, find two solutions

What angle has the cosine of negative one half? Think of 30°, 60° right triangles.

*x*= 120° or 240°Now convert the angles into radians.

See part (a).

If sin(

*x*) = 0, y = 0

Remember the side ratios of

right triangles.