# How do you solve by completing the square x^2+8x-9=0?

Mar 31, 2015

The quadratic that is a square and starts with the terms ${x}^{2}$ and $8 x$
is ${x}^{2} + 8 x + 16$

Re-write the given equation with the square quadratic at the beginning
${x}^{2} + 8 x + 16 - 25 = 0$

${\left(x + 4\right)}^{2} = 25$

$x + 4 = \pm \sqrt{25}$

$x = - 4 \pm 5$

$x = - 9$ or $x = 1$