# Math Help - Solve this identity

1. ## Solve this identity

Looking for some help!!!

Have been asked to solve the following:

"If sin13=p and cos12 = q express sin 25 in terms of p and q."

Have got this far

sin25
= sin (13+12)
= sin13cos12 + cos13sin12
= p.q + ?

Now what ?

All ideas welcomed

Thanks

2. Originally Posted by statsnewbie
Looking for some help!!!

Have been asked to solve the following:

"If sin13=p and cos12 = q express sin 25 in terms of p and q."

Have got this far

sin25
= sin (13+12)
= sin13cos12 + cos13sin12
= p.q + ?

Now what ?

All ideas welcomed

Thanks
pfft. I guess you could use that $\cos x = \pm \sqrt{1 - \sin^2 x}$ and $\sin x = \pm \sqrt {1 - \cos^2 x}$

take the appropriate signs based on what quadrant you are in