text: alright;\nnow 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.\nhypotnenuse length =?\naltitude = length of side of cube = 4\nbase = ?\n\nlets 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:\nbase = sqrt(4*4 + 4*4)= sqrt(16 +16) =sqrt(32)\nlets leave it as such for now;\nnow for the body diagonal, we again apply pythagoras theorem whihc gives us:\ndiagonal = sqrt(4*4 + 32)= sqrt(16 + 32) = sqrt(48)\n         = 6.93 inches (approx.)\n\nims 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.