Question

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sin(B + C).sin(B – C) is equal to​

Answer 1

Answer:

cosA-cosB= -2sin(A+B/2)sin(A-B/2)

So, -(cos2B-cos2C)=2sin(B+C)sin(B-C)

So, sin(B+C)sin(B-C)=1/2(cos2C-cos2B)