X2+9x=12

Solution for X2+9x=12 equation:

X2+9X=12

We move all terms to the left:

X2+9X-(12)=0

We add all the numbers together, and all the variables

X^2+9X-12=0

a = 1; b = 9; c = -12;
Δ = b2-4ac
Δ = 92-4·1·(-12)
Δ = 129
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(9)-\sqrt{129}}{2*1}=\frac{-9-\sqrt{129}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+\sqrt{129}}{2*1}=\frac{-9+\sqrt{129}}{2}
$