Prove that the true-strain rate in drawing or extrusion in plane strain with a wedge-shaped die is given by the expression where is the die angle, is the original thickness, and x is the distance...

Prove that the true-strain rate

in drawing or extrusion in plane strain with a wedge-shaped die is given by the expression

where

is the die angle,

is the original thickness, and x is the distance from die entry (Hint: Note that d
= dA/A.)