The two most common measurements of angles are degrees and radians. Remember from Technical Mathematics 1 that a degree is of a circle, and a radian is of a circle. An entire circle contains 360° or radians.

To convert from degrees to radians, multiply the number of degrees by
rad/degree

To convert from radians to degrees, multiply the number of radians by
degrees/radian

Convert 72° to radians

Convert radians to degrees

We can evaluate trigonometric functions which are in degrees or radians. If you are using a calculator, remember to have it in the proper mode.

1)

2)

3) cos = -0.9135
(You are trying to find what is)
= -142.5° or 217.5°