405=x*5*x

Solution for 405=x*5*x equation:

405=x*5x

We move all terms to the left:

405-(x*5x)=0

We add all the numbers together, and all the variables

-(+x*5x)+405=0

We get rid of parentheses

-x*5x+405=0

Wy multiply elements

-5x^2+405=0

a = -5; b = 0; c = +405;
Δ = b2-4ac
Δ = 02-4·(-5)·405
Δ = 8100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{8100}=90$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-90}{2*-5}=\frac{-90}{-10}
=+9
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+90}{2*-5}=\frac{90}{-10}
=-9
$