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Expressing the limits of integration for radius in polar coordinates

  1. Nov 7, 2013 #1
    i'm trying to integrate some some function bounded by the x-y domain of x2+y2=6y

    which is a circle on the x-y plane shifted upward where the outer part of the circle is 6.

    i'm trying to integrate a double integral.. ∫∫f(x)rdrdθ

    i don't know how to express my limits of integration for r.

    the only thing i can think of is going from 3 to 6 but then this means that i have a radius three units long going to a radius of 6 units long. what i'm looking for is a radius 0 units long to radius 3 units long, i just need this shifted up 3 units. how do i express my limits of integration for the r component?

    thanks
     
  2. jcsd
  3. Nov 7, 2013 #2

    ehild

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    You can choose the origin of he polar system of coordinates at (0,3), and change the variable y to u=y-3 in the integrand.

    ehild
     
  4. Nov 7, 2013 #3

    LCKurtz

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    You don't need to shift the origin. Write the equation ##x^2+y^2=6y## in polar coordinates to get a simple polar equation in the form ##r = f(\theta)##, which will give you the ##r## bounds.
     
    Last edited: Nov 7, 2013
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