x2+18x+81=9

Solution for x2+18x+81=9 equation:

x2+18x+81=9

We move all terms to the left:

x2+18x+81-(9)=0

We add all the numbers together, and all the variables

x^2+18x+72=0

a = 1; b = 18; c = +72;
Δ = b2-4ac
Δ = 182-4·1·72
Δ = 36
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{36}=6$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(18)-6}{2*1}=\frac{-24}{2}
=-12
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(18)+6}{2*1}=\frac{-12}{2}
=-6
$