# Thread: Trig

1. ## Trig

If sinx/siny=1/2 and cos x/cosy=3 provethat
sin(x+y)=7/3 sin x cosx

2. Originally Posted by Tiger
If sinx/siny=1/5 and cos x/cosy=3 provethat
sin(x+y)=7/3 sin x cosx
I don't think what you wrote is correct

sin(x + y) = sin(x)cos(y) + sin(y)cos(x)

replacing cos(y) and sin(y) with their equivalent expressions from the given equations, we can write sin(x + y) in terms of sin(x)cos(x). But the answer you gave won't be the right one.

3. Yeah made a mistake.

4. Originally Posted by Tiger
Yeah made a mistake.
ok, well, do as i said and you will get the answer.