.3x^2=400

Solution for .3x^2=400 equation:

.3x^2=400

We move all terms to the left:

.3x^2-(400)=0

a = .3; b = 0; c = -400;
Δ = b2-4ac
Δ = 02-4·.3·(-400)
Δ = 480
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:

$\sqrt{\Delta}=\sqrt{480}=\sqrt{16*30}=\sqrt{16}*\sqrt{30}=4\sqrt{30}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-4\sqrt{30}}{2*.3}=\frac{0-4\sqrt{30}}{0.6}
=-\frac{4\sqrt{30}}{0.6}
=-\frac{\sqrt{30}}{0.15}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+4\sqrt{30}}{2*.3}=\frac{0+4\sqrt{30}}{0.6}
=\frac{4\sqrt{30}}{0.6}
=\frac{\sqrt{30}}{0.15}
$