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Thread: Need help with integral

  1. March 23rd 2010, 10:24 PM #1
    physicalpsychics
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    Need help with integral

    Whole question:

    Compute the area of the part of the surface z = x^2 - y^2 between the cylinders x^2 + y^2 = 1 and x^2 + y^2 = 2.

    I've done the work to come up with the integral of

    <br /> \int_{1}^{2}\int_{\sqrt[]{1-x^{2}}}^{\sqrt[]{2-x^{2}}} \sqrt[]{4x^{2}+4y^{2}+1}dydx<br />

    and I'm not sure how to go about solving this. Trig sub? of what exactly? and then...
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  2. March 23rd 2010, 10:54 PM #2
    Haven
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    Convert to cylindrical coordinates.
    x = r \cos{t}
    y = r \sin{t}
    z = z

    but keep in mind that dydx becomes rdrd\theta
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