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Math Help - torus

  1. #1
    Newbie
    Joined
    Oct 2009
    Posts
    13

    torus

    Hi , I'm having trouble with this problem:

    Recall the formula for the volume of a torus (doughnut) with circular cross–section of radius
    a rotated about a vertical axis a
    distance
    b > a from its centre is 2pi(squared)a(squared)b. Suppose a + b = 3 in, inches say, what value

    of
    a will maximise the volume of the torus?

    Help!
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  2. #2
    Super Member malaygoel's Avatar
    Joined
    May 2006
    From
    India
    Posts
    648
    Quote Originally Posted by dannyshox View Post
    Hi , I'm having trouble with this problem:

    Recall the formula for the volume of a torus (doughnut) with circular cross–section of radius
    a rotated about a vertical axis a
    distance
    b > a from its centre is 2pi(squared)a(squared)b. Suppose a + b = 3 in, inches say, what value

    of
    a will maximise the volume of the torus?

    Help!
    Just substotute a=3-b in the expression of volume, then different it (with respect to b) to get the value of b for which volume is maximum.
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