Quote by Dick
It's not really all that much about the equation of the spheres. If the distance between A and B is greater then 5, then the spheres don't intersect. If it's less than 5 then they do. It's about the distance between A and B.

Ah, why don't I think about it.....
OK let's move on to find part (c). Actually I don't know which circle the question is referring to. I have image in my head that the intersection between two spheres are another 3 dimensional object, not a 2 dimensional object such as circle....