A rectangular sheet of pig pericardium, the connective tissue sac around the heart is subjected to biaxial mechanical testing prior to its fabrication into an artificial bio- prosthetic heart valve. The sheet has unloaded dimensions L and L2 (in the directions parallel to the X and X2 axes, respectively) and thickness H. The deformed configu- ration of the sheet is given by: X1 x = 1X1, x2 = 2X2, x3=3X3 Use Nanson's formula to compute the ratio of the deformed to undeformed area for the surface whose deformed outward normal is n = (1/3,1/3,1/3)T.