x*0.4x=250

Solution for x*0.4x=250 equation:

x*0.4x=250

We move all terms to the left:

x*0.4x-(250)=0

Wy multiply elements

0x^2-250=0

We add all the numbers together, and all the variables

x^2-250=0

a = 1; b = 0; c = -250;
Δ = b2-4ac
Δ = 02-4·1·(-250)
Δ = 1000
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:

$\sqrt{\Delta}=\sqrt{1000}=\sqrt{100*10}=\sqrt{100}*\sqrt{10}=10\sqrt{10}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-10\sqrt{10}}{2*1}=\frac{0-10\sqrt{10}}{2}
=-\frac{10\sqrt{10}}{2}
=-5\sqrt{10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+10\sqrt{10}}{2*1}=\frac{0+10\sqrt{10}}{2}
=\frac{10\sqrt{10}}{2}
=5\sqrt{10}
$