trig

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If tan y = -4/3 and y is in Q I'VE find cos 2y

  • trig -

    well, you know that
    siny = 3/5
    cos2y = 1 - 2sin^2 y

    or, you know that

    tan 2y = 2tany/(1-tan^2 y)
    and sec^2 2y = 1 + tan^2 2y

    good way to check your answer.

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