cos(A+B) + cos(A-B) is equal to
A) 2cosAcosB B) 2sinAsinB C) 2sinAcosB D) 2cosAsinB
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Answer:
cos (A+ B ) = cos A cos B - sin A sin B
cos (A - B) = cos A cos B + sin A sin B
therefore cos (A + B) + cos ( A - B) =
cos A cos B - sin A sin B + cos A cos B + sin A sin B
=> 2 cos A cos B
option A
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