# Thread: if sin theta....

1. ## if sin theta....

If sin theta = -3/5 and pi <theta <3pi/2, then tan theta = ?

Can someone please show me how to work this? The only thing I know about this is:
SOH, CAH, TOA
That's really it. I dont know what theta is or how to solve this. it's an ACT problem in one of these practice tests.

2. Find $\cos\theta=\pm\sqrt{1-\sin^2\theta}$.
Then use this to compute $\tan\theta$.

3. Originally Posted by vemrygh
Find $\cos\theta=\pm\sqrt{1-\sin^2\theta}$.
Then use this to compute $\tan\theta$.
so then $\cos\theta=\pm\sqrt{1-\-3/5^2\theta}$.
cos theta = sqrt[1-(9/25)]
cos theta = sqrt(16/25) ??
cos theta = -4/5
am i on the right track?

4. Yeah. It is correct of you to choose the negative solution of cosine instead of the positive since cosine is negative in the 3.quadrant.