If two carts collide on a low-friction track, it is possible for both carts to slow down. Yet Eq. \(4.1\left(\frac{m_{1}}{m_{3}}=-\frac{\Delta v_{c x}}{\Delta n_{a x}}\right)\) seems to say that, because inertia is always positive, if one velocity increases, the other must decrease. Explain the apparent discrepancy.