1. The problem statement, all variables and given/known data Sphere with P as centre has equation (x-5)^2 + (y-9)^2 + z^2 -100 = 0 Sphere with Q as centre has equation (x-1)^2 + (y+3)^2 + (z-3)^2 -49 =0 These spheres intervine with each other. Find the surface area of the object limited by the two spheres. 3. The attempt at a solution Allright, the spheres have centres in P and Q. |PQ|=|[-4,-12,3]|=13. Radius of sphere P is 10, of sphere Q 7. Here's a picture of the situation http://cameroid.com/i/JMJ80-A1 . Just read the letters from right to left and u should be good. The yellowish thing is supposed to represent the intervined part of the two spheres. I need to find the distance PS but I don't know how. I tried proving that the triangle contains 3 proportional triangles but I don't think that's the case..