# Math Help - trigonometry

1. ## trigonometry

Solve equation sin(x + 15 ) = 3cos(x - 15) for 0 - 360 degrees.

I started with

sinx cos15 + cosx sin15 = 3( cosx cos15 + sinx sin15)

i don't know where to go now

thanks
g

2. Originally Posted by gracey
Solve equation sin(x + 15 ) = 3cos(x - 15) for 0 - 360 degrees.

I started with

sinx cos15 + cosx sin15 = 3( cosx cos15 + sinx sin15)

i don't know where to go now

thanks
g
Put all the terms with $\sin x$ on one side and all the terms with $\cos x$ on the other. Then factor out $\sin x$ and $\cos x$ from their respective sides, so you get something like:

$\sin x(\cos 15 - 3\sin 15) = \cos x(3 \cos 15-\sin 15)$

Now assuming $x \ne 90^o$ and $x \ne 270^o$, divide everything by $\cos x$, and you'll need to remember a very well known trig identity here to complete the final step.