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posted by Anonymous on Thursday, January 20, 2011 at 2:55am.
cos A = -4/5 for angle A in Quadrant II, find sin 2A
in Q2 sine is negative sin^2 + cos^2 = 1 sin^2 = 1 - 16/25 = 9/25 sin = +/- 3/5 so sin A = -3/5 sin 2A = 2 sin A cos A =2 (-3/5)(-4/5) = 24/25
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