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Math Help - converting rectangular equations into polar form

  1. #1
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    converting rectangular equations into polar form

    rectangular equation : x^2 - y^2 = 4

    use the double angle forumla


    i have no idea what to do?
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  2. #2
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    Converting to a polar equation

    Hello tomatoes
    Quote Originally Posted by tomatoes View Post
    rectangular equation : x^2 - y^2 = 4

    use the double angle forumla


    i have no idea what to do?
    Using x = r\cos\theta, y = r\sin\theta, we get:

    r^2\cos^2\theta - r^2\sin^2\theta = 4

    \Rightarrow r^2(\cos^2\theta - \sin^2\theta) = 4

    But, using the double-angle formula, \cos^2\theta - \sin^2\theta = \cos2\theta, this becomes

    r^2\cos2\theta = 4

    or r^2 = 4\sec2\theta

    Grandad
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