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Sphere intersection (Posted on 2024-10-04) Difficulty: 3 of 5
Sphere (x+2)2+(y+3)2+(z+2)2=25 and (x+2)2+(y+3)2+(z-4)2=16 intersect at a circle.

What is the radius of this circle of contact?

No Solution Yet Submitted by Danish Ahmed Khan    
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Solution Solution | Comment 1 of 3
The answer is the same as for these 2 spheres:
x^2 + y^2 + (z-0)^2 = 25 and 
x^2 + y^2 + (z-6)^2 = 16

The cross section through the x-z plane is:
x^2 + (z-0)^2 = 25 and 
x^2 + (z-6)^2 = 16
wlog, re-label z as y

25 - y^2 = 16 - (y-6)^2
25 - y^2 = 16 - y^2 + 12y - 36
12y = 45
y = 15/4
x^2 = 25 - 225/16 = 175/16
x = √(175/16) = (5/4)√7 =~ 3.307189

Going back to the z terminology and the original equations, one of the intersection points of the 2 spheres is:
((5/4)√7 - 2 , -3 , 7/4)

The radius of the intersecting circle is:
   (5/4)√7 =~ 3.307189

https://www.desmos.com/calculator/kskqqxjs3h

  Posted by Larry on 2024-10-04 12:48:48
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