allerysin(A) + sin(B) equals (sum-to-product):
A2 cos((A+B)/2) sin((A-B)/2)
Bsin(A+B)
Ccos((A-B)/2)
D2 sin((A+B)/2) cos((A-B)/2)
Answer & Solution
Correct answer: D. 2 sin((A+B)/2) cos((A-B)/2)
**Sum-to-product:** sinA + sinB = 2 sin((A+B)/2) cos((A-B)/2).
(Similarly cosA + cosB = 2 cos((A+B)/2) cos((A-B)/2).)
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