(3x)(x+40)=360

Solution for (3x)(x+40)=360 equation:

(3x)(x+40)=360

We move all terms to the left:

(3x)(x+40)-(360)=0

We multiply parentheses

3x^2+120x-360=0

a = 3; b = 120; c = -360;
Δ = b2-4ac
Δ = 1202-4·3·(-360)
Δ = 18720
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:

$\sqrt{\Delta}=\sqrt{18720}=\sqrt{144*130}=\sqrt{144}*\sqrt{130}=12\sqrt{130}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(120)-12\sqrt{130}}{2*3}=\frac{-120-12\sqrt{130}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(120)+12\sqrt{130}}{2*3}=\frac{-120+12\sqrt{130}}{6}
$