Question 641343
sin 8x cos 7x - cos 8x sin 7x = 0 
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Formula: sin(x-y) = sinx*cosy - cosx*siny
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Your problem:
sin 8x cos 7x - cos 8x sin 7x = 0 
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sin(8x-7x) = 0
sin(x) = 0
x = 0 or pi or 2pi etc.
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Cheers,
Stan H.