0.9=0.1*x^2

Solution for 0.9=0.1*x^2 equation:

0.9=0.1x^2

We move all terms to the left:

0.9-(0.1x^2)=0

We get rid of parentheses

-0.1x^2+0.9=0

a = -0.1; b = 0; c = +0.9;
Δ = b2-4ac
Δ = 02-4·(-0.1)·0.9
Δ = 0.36
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-\sqrt{0.36}}{2*-0.1}=\frac{0-\sqrt{0.36}}{-0.2}
=-\frac{\sqrt{}}{-0.2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{0.36}}{2*-0.1}=\frac{0+\sqrt{0.36}}{-0.2}
=\frac{\sqrt{}}{-0.2}
$