Answer
$x\approx2.82$,
$x\approx-1.07$
Work Step by Step
$-4x^2+7x-8=-20$
$-4x^2+7x-8+20=0$
$-4x^2+7x+12=0$
$4x^2-7x-12=0$
Comparing it with standard quadratic equation
$ax^2+bx+c+0$
$a=4,b=-7,c=-12$
$x=\frac{-b \pm \sqrt { b^2-4ac}}{2a}$
$x=\frac{7 \pm \sqrt { (-7)^2-4(4)(-12)}}{2(4)}$
$x=\frac{7 \pm \sqrt { 241}}{2(4)}$
$x\approx2.82$,
$x\approx-1.07$
