Philip P. answered 04/28/15
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Effective and Patient Math Tutor
sin x/(1+cos x) = (1-cos x)/sin x
sin x = (1+cos x)(1-cos x)/sin x
sin x = (1 - cos2 x)/sin x
Use the Pythagorean Identity sin2 x + cos2 x = 1, so sin2 x = 1-cos2 x
sin x = sin2 x/sin x
sin x = sin x
QED