$2.$ PROVE Mathematically that if the same cylinder is under axial tension, the optimum axial true stain is equal to the strain hardening exponent$/$component$,$ n$,$ of the workpiece material properties when the external axial force, F$,$ reaches a maximum for the useful deformation of the cylinder. Hints: Draw the true stress$-$strain curve of a ductile material; show on it where the force F is maximum and find the corresponding optimum true strain. Use also the concepts Volume Constancy and Ludwik's Law $($stress$-$strain relationship$).$