0=-a^2-2a+26

Solution for 0=-a^2-2a+26 equation:

0=-a^2-2a+26

We move all terms to the left:

0-(-a^2-2a+26)=0

We add all the numbers together, and all the variables

-(-a^2-2a+26)=0

We get rid of parentheses

a^2+2a-26=0

a = 1; b = 2; c = -26;
Δ = b2-4ac
Δ = 22-4·1·(-26)
Δ = 108
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:

$\sqrt{\Delta}=\sqrt{108}=\sqrt{36*3}=\sqrt{36}*\sqrt{3}=6\sqrt{3}$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-6\sqrt{3}}{2*1}=\frac{-2-6\sqrt{3}}{2}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+6\sqrt{3}}{2*1}=\frac{-2+6\sqrt{3}}{2}
$