Find the value of sin 13x + sin x if cos 12x = cos 14 x
we know if cosx=cosα,x=2nπ±α
We are given cos 12x = cos 14 x
12x=2nπ±14x
We will split this into
12x=2nπ+14x or 12x=2nπ−14x
⇒x=−nπ or 13x=nπ
⇒sinx=sin(−nπ)=0and sin(13x)=sin(nπ)=0
⇒sinx+sin13x=0