quasi-static adiabatic expansion

sm09

a gas follows the equation:
PV=RT +kP

k= constant
P=pressure
V= volume
T= temperature
R= ideal gas constant

show that the work done by the gas in quasi-static adiabatic expansion can be expressed as

W= CvT1 [1- (V1-k/V2-k)^R/Cv]

V1= inital volume
V2= final volume
T1= inital temperature
Cv= specific heat of the gas at a constant volume (not temperature dependant)