5x(x+12)=20

Solution for 5x(x+12)=20 equation:

5x(x+12)=20

We move all terms to the left:

5x(x+12)-(20)=0

We multiply parentheses

5x^2+60x-20=0

a = 5; b = 60; c = -20;
Δ = b2-4ac
Δ = 602-4·5·(-20)
Δ = 4000
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:

$\sqrt{\Delta}=\sqrt{4000}=\sqrt{400*10}=\sqrt{400}*\sqrt{10}=20\sqrt{10}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(60)-20\sqrt{10}}{2*5}=\frac{-60-20\sqrt{10}}{10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(60)+20\sqrt{10}}{2*5}=\frac{-60+20\sqrt{10}}{10}
$