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| Math Central | Quandaries & Queries |
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Question from Tehmas, a student: Prove sinC+sinD=2sin(C+D/2)cos(C-D/2) |
Hi Tehmas,
I can help you get started.
Write the expression for $\sin(A + B).$
Write the expression for $\sin(A - B).$
Add the two expressions.
Harley
Tehmas responded
I don't get it
Start with the expression
\[\sin (A + B) = \sin A \cos B + \cos A \sin B\]
then use this to find an expression for $\sin (A - B) = \sin(A + (-B)).$ Add these expressions to obtain a formula for $\sin(A + B) + \sin(A - B).$
Harley
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