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Question
Express the following as a product
cos 35° – cos 75°
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Solution
We know sin C + sin D = `2 sin ("C" + "D")/2 * sin ("D" - "C")/2`
Take C = 35°, D = 75°
cos 35° – cos 75° = `2sin((35^circ + 75^circ)/2) * sin((75^circ - 35^circ)/2)`
cos 35° – cos 75° = `2sin(110^circ/2) * sin(40^circ/2)`
cos 35° – cos 75° = 2 sin 55° sin 20°
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