-5x(4x+9)=12

Solution for -5x(4x+9)=12 equation:

-5x(4x+9)=12

We move all terms to the left:

-5x(4x+9)-(12)=0

We multiply parentheses

-20x^2-45x-12=0

a = -20; b = -45; c = -12;
Δ = b2-4ac
Δ = -452-4·(-20)·(-12)
Δ = 1065
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{-(-45)-\sqrt{1065}}{2*-20}=\frac{45-\sqrt{1065}}{-40}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-45)+\sqrt{1065}}{2*-20}=\frac{45+\sqrt{1065}}{-40}
$