Answer
$ 13x - \frac{1}{2}x^{2} + C $
Work Step by Step
$\int (13-x) dx $
= $\int 13 dx - \int x dx $
= $ \int 13x^{0} dx - \frac{x^{1+1}}{1+1} + C'$
= $ \frac{13x^{1}}{1} - \frac{x^{2}}{2} + + C $
= $ 13x - \frac{1}{2}x^{2} + C $
The result can be checked by differentiating, and it works.
