text: what is the length of the diagonal of a cube if the sides are 4 inches long, please explain.  mom needs help? hey this is the mom trying to explain some homework.  so what i need is someone to explain how to find the length of the diagonal of a cube if the sides are 4 inches long.  please explain. alright; now if you imagine a cube in 3 dimensional space with one of its body diagonals(passingthrough the body of the cube), you will notie that it forms the hypotnenuse of a right angled triangle with one of the sides of the cube as the altitude and the face diagonal of the bottom face of the cube a the base. hypotnenuse length =? altitude = length of side of cube = 4 base = ?  lets find the base length. the bae itself if a face diagonal for the lower face. so it forms the hypotnenuse of a right angled triangle with two of the sides of the cube as the other sides. applying pythagoras theorem, we gt: base = sqrt(4*4 + 4*4)= sqrt(16 +16) =sqrt(32) lets leave it as such for now; now for the body diagonal, we again apply pythagoras theorem whihc gives us: diagonal = sqrt(4*4 + 32)= sqrt(16 + 32) = sqrt(48)          = 6.93 inches (approx.)  ims orry if my explanation was complex but its really hard to explain 3-d figures in words. good luck teaching your kid. if you really need the diagram, feel free to email me and i shall send it in the mail.