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Representing a Cardioid

  1. Mar 9, 2010 #1
    1. The problem statement, all variables and given/known data

    Show that the cardioid r=a(1+cos(theta)) can be represented by r=2acos2(theta/2), 0<=theta<=2pi (theta is between 0 and 2pi).

    2. Relevant equations

    3. The attempt at a solution

    I'm pretty sure I have to equate the two expressions, but I haven't been able to do this. Then I thought of converting both of them to cartesian form (and seeing if they have the same equation) but that's turning into a bit of a mess. Any guidance would be greatly appreciated!
  2. jcsd
  3. Mar 9, 2010 #2
    Those are trig functions. There are lots of identities involving trig functions. One of them might be helpful.
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