The problem is that 0.48 isn't the exact answer. It's only a numerical approximation.
A better approximation is 0.4895363 but even this isn't exact. The exact answer is irrational and doesn't have a closed form solution in terms of surds and logs and whatnot.
If you just wanted to find a numerical approximation however, there are quite a few tools you can use, such as the Newton-Raphson Method.