i want to find the max of a function f, I take that first derivative and solve the equation equals to zero, so the solution is x=$sqrt((l1+l2)/(l1))$, where l1,l2 are lagrange multipliers (previous work). I have to find the max, so if I take l1<0 and l1+l2 <0 that means that this x is the optimal solution (second derivative depend on l1, so it is negative). Is this thought correct? f:=$-l1*x+l1*z*x.^3-l2*x$
max (f)
where l1,l2 lagrange and z a constant positive value