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Question
Prove that:
sin(A + 60°) + sin(A – 60°) = sin A.
Sum
Solution
LHS = sin (A + 60°) + sin (A – 60°)
= sin A cos 60° + cos A sin 60° + sin A cos 60° – cos A sin 60°
= 2 sin A cos 60°
= 2 sin A `(1/2)`
= sin A
= RHS
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Trigonometric Ratios of Compound Angles
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