X2+12x-405=0

Solution for X2+12x-405=0 equation:

X2+12X-405=0

We add all the numbers together, and all the variables

X^2+12X-405=0

a = 1; b = 12; c = -405;
Δ = b2-4ac
Δ = 122-4·1·(-405)
Δ = 1764
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1764}=42$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(12)-42}{2*1}=\frac{-54}{2}
=-27
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(12)+42}{2*1}=\frac{30}{2}
=15
$