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Math Help - Surface Area

  1. #1
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    Surface Area

    Find the area of the surface obtained by rotating the circle x^2 + y^2 = a^2 about the line y=a.

    The y=a confuses me. What's the answer?
    Last edited by jamessmith; October 10th 2009 at 05:38 PM.
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  2. #2
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    Quote Originally Posted by jamessmith View Post
    The y=a confuses me. What's the answer?


    Did ya at least give it a shot?

    Nothing has changed here. Note that this is a circle with radius a (So... wherre will y=a be?). Also, when you differentiate, treat a like the constant that it is.

    You can do this.
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    Quote Originally Posted by jamessmith View Post
    Find the area of the surface obtained by rotating the circle x^2 + y^2 = a^2 about the line y=a.

    The y=a confuses me. What's the answer?
    Translate everything down by a units. Therefore rotate x^2 + (y + a)^2 = a^2 around the x-axis (I assume you know the formula for doing this).
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