-a^2-6a+8=0

Solution for -a^2-6a+8=0 equation:

-a^2-6a+8=0

We add all the numbers together, and all the variables

-1a^2-6a+8=0

a = -1; b = -6; c = +8;
Δ = b2-4ac
Δ = -62-4·(-1)·8
Δ = 68
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{68}=\sqrt{4*17}=\sqrt{4}*\sqrt{17}=2\sqrt{17}$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-6)-2\sqrt{17}}{2*-1}=\frac{6-2\sqrt{17}}{-2}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-6)+2\sqrt{17}}{2*-1}=\frac{6+2\sqrt{17}}{-2}
$