Hello, Here is my what am trying to solve. Express the edge length of a cube as a function of the cubes diagonal. Then express the area as a function of diagonal length if the side is x. This is what i know. The area of a cube is 6x^2 where x is the length. But in the problem i have to express the side length as a function of cubes diagonal. Can someone suggest me the relation between the side length and the diagonal, thanks.