Prove that `(cos  x +  cos y)^(2) + (sin x + sin y)^(2)  = 4 cos^(2) ((x-y)/(2))`
Channel: Doubtnut
Date: 2020-04-19

Prove that `(cos  x +  cos y)^(2) + (sin x + sin y)^(2)  = 4 cos^(2) ((x-y)/(2))`