A system goes from A to B via two processes I and II as shown in the figure. If $\Delta U_1$ and $\Delta U_2$ are the changes in internal energies in the processes I and II respectively, then:

Internal energy ($U$) is a state function. This means the change in internal energy ($\Delta U$) depends only on the initial and final states of the system and is independent of the path taken.Since both processes I and II start at state A and end at state B, the change in internal energy must be the same for both.
$$\Delta U_1=\Delta U_2$$