5x(4+4x)=120

Solution for 5x(4+4x)=120 equation:

5x(4+4x)=120

We move all terms to the left:

5x(4+4x)-(120)=0

We add all the numbers together, and all the variables

5x(4x+4)-120=0

We multiply parentheses

20x^2+20x-120=0

a = 20; b = 20; c = -120;
Δ = b2-4ac
Δ = 202-4·20·(-120)
Δ = 10000
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{10000}=100$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-100}{2*20}=\frac{-120}{40}
=-3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+100}{2*20}=\frac{80}{40}
=2
$