# Wave Equation Descending from 2D to 1D

I am stuck deriving the familiar d'Alembert formula using the Method of Descent, going from 2D to 1D. After using Kirchhoff's Formula, writing the solution independently of $y$ and some manipulations, I have obtained the following result. $$\frac{1}{2\pi c} \int_{x-ct}^{x+ct} \frac {g(x)} {({(ct)^2} - x^2)^{(1/2)}}dx$$

Where the initial conditions are $f(x) \equiv 0$ and $u_t = g(x)$.

How do I further reduce the integral to the familiar equation: $${u(x,t) = \frac{1}{2c} \int_{x-ct}^{x+ct}g(\overline{x}) d\overline{x}}$$

It is very close to the desired result, but the next step escapes me at this moment. Should I consider Polar coordinates or a change of variables?