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Homework Help: Lagrange problem

  1. Mar 12, 2009 #1
    Hi, I am supposed to find the point on the cone z^2=x^2+y^2 which is closest to the point(9,12,5).

    here is my work:


    Is it correct so far?

    If it is: I get stuck when trying to solve the equations z^2=x^2+y^2, x=9/12*y, and -2xz+9z+5x=0. Can someone please give me some advice?
  2. jcsd
  3. Mar 12, 2009 #2


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    Science Advisor
    Homework Helper

    It looks to me like you are on the right track. Now use the second equation to eliminate x or y. It will work. Just keep going.
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