find the value of : sin(n+1)x.sin(n+2)x+cos(n+1)x.cos(n+2)x

Asked by  | 2nd Mar, 2013, 09:54: AM

Expert Answer:

Since sinA.sinB + cosA.cosB = cos (A-B)
so, here  sin(n+1)x.sin(n+2)x+cos(n+1)x.cos(n+2)x    = cos ( (n+2)x - (n+1)x )
= cos(x) 

Answered by  | 2nd Mar, 2013, 10:01: AM

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