Optimal dimensions of a cylinder to minimize heat losses

The method to compute a cylinder's surface is shown in equation (1). It is the surface of the cylinder wall and twice the area of its cross-section, one for the bottom and one for the top. The formula to calculate volume, which is the cross-section times the height of the cylinder, is shown in equation (2). The height is stated as a function of the cylinder's volume V in equation (3), which is obtained by rearranging formula (2). In formula (4), the height h is substituted by the function defined in formula (3).  Formula (4) is then condensed to formula (5).