Write a value

we know that $\int \sqrt{x^{2}-a^{2}} d x=\frac{x \sqrt{x^{2}-a^{2}}}{2}-\frac{a^{2}}{2} \log \left|x+\sqrt{x^{2}-a^{2}}\right|+c$

Given $\int \sqrt{x^{2}-9} d x$

$=\int \sqrt{x^{2}-3^{2}} d x$

$=\frac{x \sqrt{x^{2}-3^{2}}}{2}-\frac{3^{2}}{2} \log \left|x+\sqrt{x^{2}-3^{2}}\right|$

$=\frac{x \sqrt{x^{2}-9}}{2}-\frac{9}{2} \log \left|x+\sqrt{x^{2}-9}\right|+c$