Question

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

Answer 1

Step-by-step explanation:

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

⇒cos[(n+2)x−(n−1)x]

{∵cos(A−B)=sinAsinB+cosAcosB}

⇒cos[(n+2−n−1)x]

⇒cos x

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