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cos A = -4/5 for angle A in Quadrant II, find sin 2A

  • trig -

    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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