$\frac{P-2 p}{V-v}=\frac{2 p-p}{v-2 v}$

$P-2 p=V \times\left(\frac{-p}{v}\right)$

$\therefore$ equation of the line : $P=V \times\left(\frac{-p}{v}\right)+2 p$

We know that internal Energy $(U)=P V$

$U=P \times V=V \times\left(V \times\left(\frac{-p}{v}\right)+2 p\right)$

$U=-V^{2} \times\left(\frac{p}{v}\right)+2 p V$

As we go from point $A$ to point $B$ volume increases.

As volume increases internal energy initially increases and then decreases, since the internal energy as a function of volume is a downward parabola.