Question

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

x this sign is not multiple sign​

Answer 1

Step-by-step explanation:

we know that,

sinAsinB+cosAcosB=cos(A-B)

so,

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

=cos [(n+1)x-(n+2)x]

=cos (2x-x)

=cosx