x^2+6x-9=12

Solution for x^2+6x-9=12 equation:

x^2+6x-9=12

We move all terms to the left:

x^2+6x-9-(12)=0

We add all the numbers together, and all the variables

x^2+6x-21=0

a = 1; b = 6; c = -21;
Δ = b2-4ac
Δ = 62-4·1·(-21)
Δ = 120
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:

$\sqrt{\Delta}=\sqrt{120}=\sqrt{4*30}=\sqrt{4}*\sqrt{30}=2\sqrt{30}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(6)-2\sqrt{30}}{2*1}=\frac{-6-2\sqrt{30}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(6)+2\sqrt{30}}{2*1}=\frac{-6+2\sqrt{30}}{2}
$