Wrev w reversible. in this case here let's see this is it's a pressure is going down.

曲线下的面积，可逆过程的功,这个过程中。

麻省理工公开课 - 热力学与动力学课程节选

So for the reversible process, the work done is the integral under the pressure volume state function, the function of state.

对可逆过程，做的功,是压强体积态函数曲线下，的积分面积。

麻省理工公开课 - 热力学与动力学课程节选