Solution: you can just replace x by alpha according to your question
Explanation : Observe that there are n terms of cos, and, in 2n,
the no. of 2 is
also n. So, we utilise each 2 with every term of cos.
We will also use the identity :sin2θ=2sinθcosθ. Thus,
But, x=π/2n+1⇒2nx+x=π,or,2nx=π−x, so that,
The L.H.S.=sinx/sinx=1=The R.H.S