Question:
Hi,
I tried many times, but can't get to solve the following question:
sin x + sin 2x + sin 3x + sin 4x = 0
Could you show me how to develope?
Thank you very much!

Hi Elia,

You can reduce the given equation to one involving only sin x and cos
x -- just use your basic trig identities such as

sin 2x = 2(sin x)(cos
x)
sin(A + B) = sin A cos B + cos A sin B
and sin 3x = sin (2x + x) = ...