3x(9x-3)=90

Solution for 3x(9x-3)=90 equation:

3x(9x-3)=90

We move all terms to the left:

3x(9x-3)-(90)=0

We multiply parentheses

27x^2-9x-90=0

a = 27; b = -9; c = -90;
Δ = b2-4ac
Δ = -92-4·27·(-90)
Δ = 9801
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{9801}=99$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-9)-99}{2*27}=\frac{-90}{54}
=-1+2/3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-9)+99}{2*27}=\frac{108}{54}
=2
$