a^2+18a+13=0

Solution for a^2+18a+13=0 equation:

a^2+18a+13=0

a = 1; b = 18; c = +13;
Δ = b2-4ac
Δ = 182-4·1·13
Δ = 272
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:

$\sqrt{\Delta}=\sqrt{272}=\sqrt{16*17}=\sqrt{16}*\sqrt{17}=4\sqrt{17}$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(18)-4\sqrt{17}}{2*1}=\frac{-18-4\sqrt{17}}{2}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(18)+4\sqrt{17}}{2*1}=\frac{-18+4\sqrt{17}}{2}
$