### Home > CCA2 > Chapter Ch12 > Lesson 12.2.1 > Problem 12-100

12-100.

If . Use what you know about the Pythagorean Identity and the unit circle to get started.

Remember that the Pythagorean Identity is

Try substituting the given value of

Take the square root of both sides to solve for

Now use the unit circle to decide what the correct sign of the answer is.