-x2+80x+1500=0

Solution for -x2+80x+1500=0 equation:

-x2+80x+1500=0

We add all the numbers together, and all the variables

-1x^2+80x+1500=0

a = -1; b = 80; c = +1500;
Δ = b2-4ac
Δ = 802-4·(-1)·1500
Δ = 12400
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:

$\sqrt{\Delta}=\sqrt{12400}=\sqrt{400*31}=\sqrt{400}*\sqrt{31}=20\sqrt{31}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(80)-20\sqrt{31}}{2*-1}=\frac{-80-20\sqrt{31}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(80)+20\sqrt{31}}{2*-1}=\frac{-80+20\sqrt{31}}{-2}
$