x^2+12x-3=15

Solution for x^2+12x-3=15 equation:

x^2+12x-3=15

We move all terms to the left:

x^2+12x-3-(15)=0

We add all the numbers together, and all the variables

x^2+12x-18=0

a = 1; b = 12; c = -18;
Δ = b2-4ac
Δ = 122-4·1·(-18)
Δ = 216
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:

$\sqrt{\Delta}=\sqrt{216}=\sqrt{36*6}=\sqrt{36}*\sqrt{6}=6\sqrt{6}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(12)-6\sqrt{6}}{2*1}=\frac{-12-6\sqrt{6}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(12)+6\sqrt{6}}{2*1}=\frac{-12+6\sqrt{6}}{2}
$