Question

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

Answer 1

Answer:

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Answer 2

HELLO DEAR,

cos(n+1)xcos(n+2)x + sin(n+1)xsin(n+2)x

it is from the identity

cos(a-b) = cosa * cosb + sina * sinb

here a= (n+1)x b= (n+2)x

so,

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

cos(nx+x-nx-2x)

cos(-x)

cosx { since cos(-x) = cosx }

I HOPE ITS HELP YOU DEAR,

THANKS