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Math Help - Double angle formulae

  1. #1
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    Double angle formulae

    Hi, I have a question on double angle formulae:
    Eliminate theta from the equation
    x = 2 sec theta, y = cos 2 theta

    The answer is x^2y = 8 - x^2

    Thank you!
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  2. #2
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    Re: Double angle formulae

    Quote Originally Posted by sakuraxkisu View Post
    Hi, I have a question on double angle formulae:
    Eliminate theta from the equation
    x = 2 sec theta, y = cos 2 theta

    The answer is x^2y = 8 - x^2
    x = 2 \sec{\theta} \implies \cos{\theta} = \frac{2}{x}

    y = \cos(2\theta) = 2\cos^2{\theta} - 1

    proceed ...
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  3. #3
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    Re: Double angle formulae

    Thank you so much! I feel like a bit of an idiot as that was so simple haha
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