161=5x*x

Solution for 161=5x*x equation:

161=5x*x

We move all terms to the left:

161-(5x*x)=0

We add all the numbers together, and all the variables

-(+5x*x)+161=0

We get rid of parentheses

-5x*x+161=0

Wy multiply elements

-5x^2+161=0

a = -5; b = 0; c = +161;
Δ = b2-4ac
Δ = 02-4·(-5)·161
Δ = 3220
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:

$\sqrt{\Delta}=\sqrt{3220}=\sqrt{4*805}=\sqrt{4}*\sqrt{805}=2\sqrt{805}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{805}}{2*-5}=\frac{0-2\sqrt{805}}{-10}
=-\frac{2\sqrt{805}}{-10}
=-\frac{\sqrt{805}}{-5}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{805}}{2*-5}=\frac{0+2\sqrt{805}}{-10}
=\frac{2\sqrt{805}}{-10}
=\frac{\sqrt{805}}{-5}
$