A) \[\sin 2A\]
B) \[\cos 2A\]
C) \[\tan 2A\]
D) \[\cot 2A\]
Correct Answer: B
Solution :
\[\sin \,\,(n+1)A\sin \,\,(n-1)A+\cos \,\,(n+1)A\cos \,\,(n-1)A\] \[=\cos \,\,(n+1)A\cos \,\,(n-1)A+\sin \,\,(n+1)A\sin \,\,(n-1)A\]\[=\cos \,\,[(n+1)A-\,\,(n-1)A]=\cos \,\,[nA+A-nA+A]\]\[=\cos 2A\]You need to login to perform this action.
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