I want to use the FindMaximum tool to find the maximum of the function x^7/(840*L^3) - L*x^3/120 + 140*L^3*x where x is a variable and L is an undefined constant. That is I want to find the maximum of this function in terms of L. I tried FindMaximum but couldn't get it to work. Anyone know how to do this? Or can any one think of a better way? Thanks!