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The substended angle of a circle

  1. Nov 22, 2012 #1
    The subtended angle of a circle

    Hello! I came across the following formula for the change in the subtended angle (of a circle), when we move our obersvation point [tex]\vec{x}[/tex] by [tex]\delta \vec{x},[/tex]

    [tex]\delta \Omega = \oint \hat{x} \cdot \frac{(\delta \vec{x} \times d\vec{l})}{|\vec{x}|^2}. [/tex]

    The integration path is the circumference of the circle.

    Do you know any litterature or easy derivation that can prove this fact?

    Thanks for your help, really appreciated!
    Last edited: Nov 22, 2012
  2. jcsd
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