sinA+sinB=2sin(A+B/2)cos(A-B/2)咋证?

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sinA+sinB=2sin(A+B/2)cos(A-B/2)咋证?sinA+sinB=2sin(A+B/2)cos(A-B/2)咋证?sinA+sinB=2sin(A+B/2)cos(A-B/2)咋

sinA+sinB=2sin(A+B/2)cos(A-B/2)咋证?
sinA+sinB=2sin(A+B/2)cos(A-B/2)咋证?