4x(3+x)=72

Solution for 4x(3+x)=72 equation:

4x(3+x)=72

We move all terms to the left:

4x(3+x)-(72)=0

We add all the numbers together, and all the variables

4x(x+3)-72=0

We multiply parentheses

4x^2+12x-72=0

a = 4; b = 12; c = -72;
Δ = b2-4ac
Δ = 122-4·4·(-72)
Δ = 1296
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1296}=36$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(12)-36}{2*4}=\frac{-48}{8}
=-6
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(12)+36}{2*4}=\frac{24}{8}
=3
$