da/A=(1/isotropic constant of superheated steam i.e 1.3 )(dp/P)(1-m^2)(m^2) where dp=initial convergent pressure- final end of divergent nozzle pressure=p1-p3=neagtive.similarly for da=-ve. so the term (1-m2)(m2) is positive.This implies that m<1.i.e m=ratio...