3x(x+20)=40

Solution for 3x(x+20)=40 equation:

3x(x+20)=40

We move all terms to the left:

3x(x+20)-(40)=0

We multiply parentheses

3x^2+60x-40=0

a = 3; b = 60; c = -40;
Δ = b2-4ac
Δ = 602-4·3·(-40)
Δ = 4080
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:

$\sqrt{\Delta}=\sqrt{4080}=\sqrt{16*255}=\sqrt{16}*\sqrt{255}=4\sqrt{255}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(60)-4\sqrt{255}}{2*3}=\frac{-60-4\sqrt{255}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(60)+4\sqrt{255}}{2*3}=\frac{-60+4\sqrt{255}}{6}
$