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Math Help - Double Angle Formula

  1. #1
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    Exclamation Double Angle Formula

    Find the exact value of sin2x.

    Sinx = (-4/7)
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  2. #2
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    Quote Originally Posted by jumpman23 View Post
    Find the exact value of sin2x.

    Sinx = (-4/7)
    You should know from class that \sin(2x)=2\sin(x)\cos(x). You already known sin(x). To find cos(x) you can use the info already given to draw a right triangle and solve for the missing leg needed to find cos(x).
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