-x^2-6x+99=0

Solution for -x^2-6x+99=0 equation:

-x^2-6x+99=0

We add all the numbers together, and all the variables

-1x^2-6x+99=0

a = -1; b = -6; c = +99;
Δ = b2-4ac
Δ = -62-4·(-1)·99
Δ = 432
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:

$\sqrt{\Delta}=\sqrt{432}=\sqrt{144*3}=\sqrt{144}*\sqrt{3}=12\sqrt{3}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-6)-12\sqrt{3}}{2*-1}=\frac{6-12\sqrt{3}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-6)+12\sqrt{3}}{2*-1}=\frac{6+12\sqrt{3}}{-2}
$