How do I calculate work when both pressure and volume are changing?

[celtic]

i need help when trying to find the work done by a gas when the pressure and volume are BOTH changing. i know the ( W=P x (change in V) and how to solve problems when pressure is constant, but i don't know what to do when P and V both change.

please post an equation, thanks.

 

[edgepflow]

Use: dW = P(V) dV or W = Integral [ P(v) dV ]