3x(x+8)=90

Solution for 3x(x+8)=90 equation:

3x(x+8)=90

We move all terms to the left:

3x(x+8)-(90)=0

We multiply parentheses

3x^2+24x-90=0

a = 3; b = 24; c = -90;
Δ = b2-4ac
Δ = 242-4·3·(-90)
Δ = 1656
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:

$\sqrt{\Delta}=\sqrt{1656}=\sqrt{36*46}=\sqrt{36}*\sqrt{46}=6\sqrt{46}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(24)-6\sqrt{46}}{2*3}=\frac{-24-6\sqrt{46}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(24)+6\sqrt{46}}{2*3}=\frac{-24+6\sqrt{46}}{6}
$