If A = 30°, then prove that :
sin 3A = 3 sin A - 4 sin3 A
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2 cos2 A - 1 = 1 - 2 sin2 A
If A = B = 45°, show that :
sin (A - B) = sin A cos B - cos A sin B
cos (A + B) = cos A cos B - sin A sin B