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use an apropriate sum or difference indentity to prove the double-angle identity cos2u=1-2sin2u

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amber

  1. You stated the identity incorrectly , is should have been
    cos 2u = 1 - 2sin^2 u

    LS = cos 2u
    = cos(u+u) = cosucosu - sinusinu
    = cos^2 u - sin^2 u
    = (1-sin^2 u) - sin^2 u
    = 1 - 2sin^2 u
    = RS

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    Reiny

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