Find the value of tan(a-b) if cos a=-3/5, sin b=5/13, 90

Question

Find the value of tan(a-b) if cos a=-3/5, sin b=5/13,  90<a<180, and 90<b<180.
Help please quick!

myininaya · Answer

Use the difference rule for tan(a-b)

anonymous · Answer

I'm trying to catch up quickly and didn't get to this lesson. I have no idea what that means.

myininaya · Answer

What about the sin difference rule and the cosine difference rule?

anonymous · Answer

No, I didn't get to any of it. I don't know how to work it.

myininaya · Answer

$$\tan(a-b)=\frac{\sin(a-b)}{\cos(a-b)}$$
So you don't know the following identities:
$$\sin(a \pm b) =\sin(a)\cos(b) \pm \sin(b)\cos(a)$$
$$\cos(a \pm b)=\cos(a)\cos(b) \mp \sin(a)\sin(b)$$

myininaya · Answer

these are the sum and difference identities for sin and cos

anonymous · Answer

No, I don't.. Can you please tell me the answer? I'm on a time limit..

myininaya · Answer

Oh no. That isn't the way this works.

myininaya · Answer

I will help if you are willing to learn and to help yourself.

myininaya · Answer

I do not cheat though and OpenStudy does not allow cheating.