0.21=x^2

Solution for 0.21=x^2 equation:

0.21=x^2

We move all terms to the left:

0.21-(x^2)=0

We add all the numbers together, and all the variables

-1x^2+0.21=0

a = -1; b = 0; c = +0.21;
Δ = b2-4ac
Δ = 02-4·(-1)·0.21
Δ = 0.84
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{0.84}}{2*-1}=\frac{0-\sqrt{0.84}}{-2}
=-\frac{\sqrt{}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{0.84}}{2*-1}=\frac{0+\sqrt{0.84}}{-2}
=\frac{\sqrt{}}{-2}
$