.4x^2-100=0

Solution for .4x^2-100=0 equation:

.4x^2-100=0

a = .4; b = 0; c = -100;
Δ = b2-4ac
Δ = 02-4·.4·(-100)
Δ = 160
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:

$\sqrt{\Delta}=\sqrt{160}=\sqrt{16*10}=\sqrt{16}*\sqrt{10}=4\sqrt{10}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-4\sqrt{10}}{2*.4}=\frac{0-4\sqrt{10}}{0.8}
=-\frac{4\sqrt{10}}{0.8}
=-\frac{\sqrt{10}}{0.2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+4\sqrt{10}}{2*.4}=\frac{0+4\sqrt{10}}{0.8}
=\frac{4\sqrt{10}}{0.8}
=\frac{\sqrt{10}}{0.2}
$