Prove that: `sin (n + 1) x sin (n + 2)x + cos (n + 1) x cos (n + 2) x = cos x`
Channel: Doubtnut
Date: 2020-06-28

Prove that: `sin (n + 1) x sin (n + 2)x + cos (n + 1) x cos (n + 2) x = cos x`