temoalta wrote:

Could someone please explain why E is not correct?

To me, here we are dealing with a right triangle with dimensions x-x-xsqrt(2). x is the diameter of the sphere. If I subtract xsqrt(2)-x I would get the distance between two of the vertices and the sphere. Then I divide that by 2 to get just one side, and so it would be x/2(sqrt(2)-1).

We are dealing with a right triangle where the hypotenuse is the diagonal of the cube, and the legs are the edge and the diagonal of a face.

I do understand we have a right triangle. I guess I don't see what is wrong with my logic.