Lagrange multiplier allows the creation of a system of simultaneous equations formed by ...
Fx=AGx ... .5(yz)-.5 =A
Fy=AGy ... .5(xz)-.5=A
Fz=AGz ... .5(xy)-.5=A
Note from the above x=y=z ... Use this fact solve G for x=y=z =1 ... this will be the absolute maximum value of F. The absolute minimum value will be zero.