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Sphere equation from endpoints.

  1. Sep 9, 2009 #1
    Find the equation of a sphere if one of its diameters has endpoints: (-19, -15, -3) and (1, 5, 17).



    Thought it would be this, but the program web-work says its wrong.

    Lets assume my first coordinate is a (-19, -15, -3) and b is (1, 5, 17)

    I found the midpoint since I assumed that would be the center, then I found the length from my midpoint to b ,but my equation is wrong.

    (x+9)^2+(y+5)^2+(z-7)^2-640=0
     
  2. jcsd
  3. Sep 10, 2009 #2

    lanedance

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    Homework Helper

    hey graycolor, method sounds right... showing your working will help finding the problem easier...

    that said, I would check your radius
     
  4. Sep 10, 2009 #3
    I think you calculated the radius wrong.

    [tex]radius=diameter/2[/tex]

    [tex]diameter=\sqrt{(-19-1)^2+(-15-5)^2+(-3-17)^2}=\sqrt{3*20^2}=20\sqrt{3}[/tex]

    Now find the radius and then r2. :smile:
     
  5. Sep 10, 2009 #4
    Thanks guys
     
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