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Math Help - Double Angle Question W/Picture.

  1. #1
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    Double Angle Question W/Picture.

    Double Angle Question W/Picture. Attached
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  2. #2
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    Re: Double Angle Question W/Picture.

    Use the Pythagorean Identity to simplify the double angle identity you've been given so far...

    \displaystyle \begin{align*} \sin^2{(x)} + \cos^2{(x)} \equiv 1 \end{align*}, so that means

    \displaystyle \begin{align*} \cos{(2x)} &\equiv \cos^2{(x)} - \sin^2{(x)} \\ &\equiv 2\cos^2{(x)} - 1 \\ &\equiv 1 - 2\sin^2{(x)} \end{align*}
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    Re: Double Angle Question W/Picture.

    Quote Originally Posted by Melcarthus View Post
    Double Angle Question W/Picture. Attached
    Do you understand that \sin(2\alpha)=\frac{2}{5}~?

    So 2\sin(\alpha)\cos(\alpha)=\frac{2}{5}~.
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    Re: Double Angle Question W/Picture.

    Actually I think you'll find \displaystyle \begin{align*} \sin{(2\alpha)} = \frac{4}{5} \end{align*}, not \displaystyle \begin{align*} \frac{2}{5} \end{align*}.
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    Re: Double Angle Question W/Picture.

    i think Prove It is just right.
    Double Angle Question W/Picture.-03-jul-13.png
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