So mathematically we can't solve this. But if we come up with a system of equations, two equations and two unknowns, we could somehow manipulate the two equations, get rid of that C, and solve for our unknown. And in fact, that's exactly what we're going to do. Notice we have initial conditions and final conditions. So why not come up with two of these equations, one for the initial condition and one for the final condition. That's exactly what we do here.