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.