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  1. #1
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    Calculator help

    I am trying to graph r^2=2cos(2theta)
    in my answer key it's supposed to be an infinity symbol but I get a 4 leaf lemniscate. I am in polar mode so what can be the error?
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  2. #2
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    Quote Originally Posted by aaronb View Post
    I am trying to graph r^2=2cos(2theta)
    in my answer key it's supposed to be an infinity symbol but I get a 4 leaf lemniscate. I am in polar mode so what can be the error?
    If \theta lies between \pi/4 and 3\pi/4 (or between -3\pi/4 and -\pi/4) then \cos(2\theta) is negative and will not have a square root. So the top and bottom leaves of the lemniscate ought not to be there. Maybe you should rewrite the equation as r = \sqrt{2\cos(2\theta)} and see what the calculator makes of that version.
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