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Math Help - cosx = -5/13 ... find sin2x

  1. #1
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    cosx = -5/13 ... find sin2x

    cosx = -5/13 where pi/2 < x < pi find

    a) sin2x

    any idea how to do this?
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  2. #2
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    find the value of \sin{x} using the value they gave you for \cos{x} by sketching a reference triangle in quad II.

    then use the double angle identity ...

    2\sin{x} \cos{x} = \sin(2x)
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  3. #3
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    wow thank you skeet

    thought there was another way to solve it
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