Question

sin(n+1)x. sin(n+2)x + cos (n+1)x.cos(n+2)x=cos x

Answer 1

Answer:

cos(-x) = cosx

Step-by-step explanation:

cos(n+1)x * cos(n+2)x + sin(n+1)x * sin(n+2)x

cosA*cosB + sinA*sinB = cos(A-B)

cos((n+1)x - (n+2)x)

cos(nx + x - nx - 2x)

cos(x - 2x)

cos(-x) = cosx