# How do you write in vertex form for y=x^2 - 9x by completing the square?

$y = {x}^{2} - 9 x$
$y = {x}^{2} - 9 x + {\left(\frac{9}{2}\right)}^{2} - {\left(\frac{9}{2}\right)}^{2}$
$y = \left(x - \frac{9}{2}\right) - \frac{81}{4}$
which is the vertex form with the vertex at $\left(\frac{9}{2} , - \frac{81}{4}\right)$