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Homework Help: Find the equation of the sphere

  1. Aug 27, 2005 #1
    Find the equation of the sphere centered at (-6,-7,-1) with radius 9.

    well i got [tex](x+6)^2 + (y+7)^2 + (z+1)^2-9^2[/tex] which is correct.

    now for the next question:

    Give an equation which describes the intersection of this sphere with the plane [tex]z=0[/tex].

    i dont understand how to do the second question at all, can someone help?
  2. jcsd
  3. Aug 27, 2005 #2
    What you got must've been:
    [tex](x+6)^2 + (y+7)^2 + (z+1)^2-9^2 = 0[/tex].

    The equation that describes the intersection with the plane z = 0 must be:
    [tex](x+6)^2 + (y+7)^2 + (0+1)^2-9^2 = (x+6)^2 + (y+7)^2 - 80 = 0 [/tex]
  4. Aug 27, 2005 #3
    thanks alot, i get it now
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