Answer
$x=-8,1$
Work Step by Step
To complete the square, add a term that is the square of half the coefficient of $x$ to both sides of the equation, and factor the left side. Then use the square root property to simplify both sides, and then isolate $x$.
$x^2+7x-8=0$
$(\frac{7}{2})^2$
$x^2+7x-8+8+(\frac{7}{2})^2=8+(\frac{7}{2})^2$
$x^2+7x+(\frac{7}{2})^2=8+(\frac{7}{2})^2$
$x^2+7x+\frac{49}{4}=8+\frac{49}{4}$
$x^2+7x+\frac{49}{4}=\frac{81}{4}$
$(x+\frac{7}{2})^2=\frac{81}{4}$
$x+\frac{7}{2}=±\frac{9}{2}$
$x=-\frac{7}{2}±\frac{9}{2}$
$x=-8,1$
