400x-0,4x^2=0

Solution for 400x-0,4x^2=0 equation:

400x-0.4x^2=0

a = -0.4; b = 400; c = 0;
Δ = b2-4ac
Δ = 4002-4·(-0.4)·0
Δ = 160000
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{160000}=400$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(400)-400}{2*-0.4}=\frac{-800}{-0.8}
=+1000
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(400)+400}{2*-0.4}=\frac{0}{-0.8}
=0
$