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Homework Help: Find an equation of the largest sphere

  1. Jan 31, 2015 #1
    1. The problem statement, all variables and given/known data
    Find an equation of the largest sphere with center (5, 4, 9) that is contained in the first octant.

    2. Relevant equations
    x2 + y2 + z2

    3. The attempt at a solution

    (x - 5)2 + (y - 4)2 + (z - 9)2 = R2
    I am under the impression that R must be no greater than 4, is this true?
    My logic stems from the fact that the center is situated at (5, 4, 9), so it is only 4 units away from the y axis. If R > 4, then it will intersect the XZ plane. My textbook does not have answers, so I am not sure if my reasoning is valid.
  2. jcsd
  3. Jan 31, 2015 #2


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    Yes, that's correct.
  4. Feb 2, 2015 #3


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    Science Advisor

    Actually, the crucial point is that it is only 4 units away from the xz- plane.

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