# Math Help - cosx = -5/13 ... find sin2x

1. ## cosx = -5/13 ... find sin2x

cosx = -5/13 where pi/2 < x < pi find

a) sin2x

any idea how to do this?

2. find the value of $\sin{x}$ using the value they gave you for $\cos{x}$ by sketching a reference triangle in quad II.

then use the double angle identity ...

$2\sin{x} \cos{x} = \sin(2x)$

3. wow thank you skeet

thought there was another way to solve it