-8x^2-20x+9=0

Solution for -8x^2-20x+9=0 equation:

-8x^2-20x+9=0

a = -8; b = -20; c = +9;
Δ = b2-4ac
Δ = -202-4·(-8)·9
Δ = 688
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{688}=\sqrt{16*43}=\sqrt{16}*\sqrt{43}=4\sqrt{43}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-4\sqrt{43}}{2*-8}=\frac{20-4\sqrt{43}}{-16}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+4\sqrt{43}}{2*-8}=\frac{20+4\sqrt{43}}{-16}
$