5x(3x+6)=120

Solution for 5x(3x+6)=120 equation:

5x(3x+6)=120

We move all terms to the left:

5x(3x+6)-(120)=0

We multiply parentheses

15x^2+30x-120=0

a = 15; b = 30; c = -120;
Δ = b2-4ac
Δ = 302-4·15·(-120)
Δ = 8100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{8100}=90$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(30)-90}{2*15}=\frac{-120}{30}
=-4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(30)+90}{2*15}=\frac{60}{30}
=2
$