1. factoring

if anyone has a quicker way I could factor this it would be appreciated.

$\frac{1}{2}(36-2x)\sqrt{x^2 - \frac{1}{4}(36 - 2x)^2}$

$\frac{1}{2}-2(x-18)\sqrt{x^2 - \frac{1}{4}(36 - 2x)^2}$

$\frac{1}{2}-2(x-18)\sqrt{x^2 - \frac{1}{4}(4x^2 -72x + 1296)$

$\frac{1}{2}-2(x-18)\sqrt{x^2 - (x^2 - 36x + 324)}$

$\frac{1}{2}-2(x-18)\sqrt{36x+324}$

$\frac{1}{2}-2(x-18)\sqrt{36(x-9)$

$\frac{1}{2}-2(x-18)6\sqrt{x-9}$

$-6(x-18)\sqrt{x-9}$

thank you!!