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Thread: spheres -|:o)

  1. #1

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    Fanatic Member bugzpodder's Avatar
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    spheres -|:o)

    given spheres of radius 2,2,3,3 tangent to all other and a smaller sphere tangent to all 4 find its radius
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  2. #2
    l33t! MrPolite's Avatar
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    r=1?

    edit: nm way too wrong
    Last edited by MrPolite; Jan 27th, 2003 at 05:03 PM.
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    Fanatic Member alkatran's Avatar
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    I can't wait until I can understand all of this
    Tangent = straight line touching very "edge" of a circle right?? So what is a smaller sphere tangent??
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  4. #4
    vbuggy krtxmrtz's Avatar
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    Originally posted by alkatran
    So what is a smaller sphere tangent??
    One that has the same derivative at the point of tangency. Or, put it another way, both spheres share the same tangent line.

  5. #5
    vbuggy krtxmrtz's Avatar
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    Originally posted by myself
    One that has the same derivative at the point of tangency. Or, put it another way, both spheres share the same tangent line.
    My fault, should have been "same tangent plane", not "same tangent line"... and, of course, the derivative should be the partial derivatives.

  6. #6
    transcendental analytic kedaman's Avatar
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    a,b,c,d are spheres with radii 3,3,2 and 2 respectively
    first figure:
    The distance between two spheres is the sum of their radii
    the triangles c-d-e, b-a-e are isosceles with legs 2+e resp 3+e
    second figure:
    the line from c+(d-c)/2 to a+(b-a)/2 goes trough e, and is perpendicular with a-b and b-c
    their planes are perpendicular (due to symetry, can't bother explain this right now)
    third figure:
    thus a-d can be put in a box with sides 2,3 and z.
    x^2+y^2+z^2=spacediagonale
    z=sqrt(25-9-4)=sqrt(12) = sqrt((2+e)^2-2^2)+sqrt((3+e)^2-3^2)
    12=e(e+4)+e(e+6)+2sqrt(e(e+4)e(e+6))
    e=6/11
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