A sealed cylinder with a moveable piston contains a monatomic ideal gas at pressure 0 and volume 0. The gas first undergoes an isobaric expansion to a final volume 0, where is a positive constant. It then undergoes an isochoric process which decreases the pressure to 0, where is a positive constant.

Assuming both processes are quasi‑static, derive an expression for the total change in the internal energy Δtot of the gas. Express your answer in terms of 0, 0, , , and numerical constants.