(x+8)(3x-9)=672

Solution for (x+8)(3x-9)=672 equation:

(x+8)(3x-9)=672

We move all terms to the left:

(x+8)(3x-9)-(672)=0

We multiply parentheses ..

(+3x^2-9x+24x-72)-672=0

We get rid of parentheses

3x^2-9x+24x-72-672=0

We add all the numbers together, and all the variables

3x^2+15x-744=0

a = 3; b = 15; c = -744;
Δ = b2-4ac
Δ = 152-4·3·(-744)
Δ = 9153
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:

$\sqrt{\Delta}=\sqrt{9153}=\sqrt{81*113}=\sqrt{81}*\sqrt{113}=9\sqrt{113}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-9\sqrt{113}}{2*3}=\frac{-15-9\sqrt{113}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+9\sqrt{113}}{2*3}=\frac{-15+9\sqrt{113}}{6}
$