-.8x^2+20x+100=0

Solution for -.8x^2+20x+100=0 equation:

-.8x^2+20x+100=0

We add all the numbers together, and all the variables

-0.8x^2+20x+100=0

a = -0.8; b = 20; c = +100;
Δ = b2-4ac
Δ = 202-4·(-0.8)·100
Δ = 720
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:

$\sqrt{\Delta}=\sqrt{720}=\sqrt{144*5}=\sqrt{144}*\sqrt{5}=12\sqrt{5}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-12\sqrt{5}}{2*-0.8}=\frac{-20-12\sqrt{5}}{-1.6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+12\sqrt{5}}{2*-0.8}=\frac{-20+12\sqrt{5}}{-1.6}
$