3x(9+x)-8=72

Solution for 3x(9+x)-8=72 equation:

3x(9+x)-8=72

We move all terms to the left:

3x(9+x)-8-(72)=0

We add all the numbers together, and all the variables

3x(x+9)-8-72=0

We add all the numbers together, and all the variables

3x(x+9)-80=0

We multiply parentheses

3x^2+27x-80=0

a = 3; b = 27; c = -80;
Δ = b2-4ac
Δ = 272-4·3·(-80)
Δ = 1689
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(27)-\sqrt{1689}}{2*3}=\frac{-27-\sqrt{1689}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(27)+\sqrt{1689}}{2*3}=\frac{-27+\sqrt{1689}}{6}
$