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Trigonometric Substitution

  1. Feb 8, 2012 #1
    I was messing around proving the area of a circle using trigonometric substitution. However, I ended up with area = -πr^2.

    In my integral I ended up using trigonometric substitution and setting x = r*cos(theta)

    However, this yields x = -r*sin(theta)*d(theta).

    When that's substituted back into my integral, I ended up with the negative value for area. Why is it that if I were to use a different angle theta and express x = r*sin(theta) that I end up with the correct area?

    Thanks a lot, as always.
  2. jcsd
  3. Feb 9, 2012 #2


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    hi basenne! :smile:

    it's probably your limits of integration that were wrong …

    what exactly was your integral?​
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