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Question
Express the following as a product
sin 50° + sin 40°
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Solution
We know sin C + sin D = `2 sin ("C" + "D")/2 * cos ("C" - "D")/2`
Take C = 50°, D = 40°
sin 50° + sin 40° = `2sin((50^circ + 40^circ)/2) * cos((50^circ - 40^circ)/2)`
sin 50° + sin 40° = `2cos(90^circ/2) * cos(10^circ/2)`
sin 50° + sin 40° = 2 cos(45°) . cos(5°)
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