X(x+12)=9

Solution for X(x+12)=9 equation:

X(X+12)=9

We move all terms to the left:

X(X+12)-(9)=0

We multiply parentheses

X^2+12X-9=0

a = 1; b = 12; c = -9;
Δ = b2-4ac
Δ = 122-4·1·(-9)
Δ = 180
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:

$\sqrt{\Delta}=\sqrt{180}=\sqrt{36*5}=\sqrt{36}*\sqrt{5}=6\sqrt{5}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(12)-6\sqrt{5}}{2*1}=\frac{-12-6\sqrt{5}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(12)+6\sqrt{5}}{2*1}=\frac{-12+6\sqrt{5}}{2}
$