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Prove that: sin(n+1)A s in(n+2)A+cos(+1)...

Prove that: `sin(n+1)A s in(n+2)A+cos(+1)A cos(n+2)A=cos A`

Text Solution

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LHS`=sin{(n+1)A}sin{(n+2)A} + cos{(n+1)A}cos{(n+2)A}`
`cos{(n+2)A-(n+1)A}`
`=cosA=` R.H.S Hence Proved.
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