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Homework Help: Integral over a surface

  1. Aug 2, 2010 #1
    I am having problem with an integral. I dont know how to write in mathcode so excuse me for my notation.

    This is in spherical coordinates:

    x = theta
    y = psi
    r = radial component

    the integrand is: (cos(x)/r^2)

    I want to integrate this over a solid angle of an arbitrary surface.

    da is a differential area. And in spherical coordiantes should be: da = r^2*sin(x)dxdy

    I know the integral should be 4*pi but I dont get it right. I want to have the antiderivate as (cos(x)^2)/2 from 0 to pi.

    Then I get 1/2*2pi = pi

    So I am missing a factor 4 here. Can anyone help me show what I've missed?
  2. jcsd
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