Question

# Which of the following is correct:cos(A – B) = cosA cosB + sinA sinB cos(A + B) = cosA cosB + sinA sinB cos(A + B) = cosA + cosB cos(A – B) = cosA – cosB

Solution

## The correct option is A cos(A – B) = cosA cosB + sinA sinB cos(x + y) = cosx cosy – sinx siny Replacing y by –y in the above identity, we get cos (x – y) = cosx cosy + sinx siny

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