Question

Given that cos C= -5/13 with C in quadrant 2, find sin 2C

Answer 1

You need to know two (maybe three) things.

1) sin(2C)= 2 sin(C)cos(C)
2) Given cos(C), find sin(C) draw a picture. It helps.

So can you find the sin(C)?

Answer 2

I'm having a really hard time with this stuff, not too sure how to find sin c either?

Answer 3

Have you watched this (and maybe the next few videos, if you have time)
http://www.khanacademy.org/math/trigonometry/v/basic-trigonometry