Hello, littlelisa!

Cosine is negative in Quadrants 2 and 3.If , find

Tangent is negative in Quadrants 2 and 4.

. . Hence, is in Quadrant 2.

Identity: .

So we have: .

Sum-to-product identity: .Find all the solutions of in the interval

So: .

The equation becomes: .

. . Factor: .

We have two equations to solve . . .

. . Therefore: .

. . Therefore: .

Product-to-sum identity: .Rewrite as a sum.

Therefore: .

You left out part of theFind all the solutions of in the intervalequation. . .