x(x*0.25)=400

Solution for x(x*0.25)=400 equation:

x(x*0.25)=400

We move all terms to the left:

x(x*0.25)-(400)=0

We add all the numbers together, and all the variables

x(+x*0.25)-400=0

We multiply parentheses

0.25x^2-400=0

a = 0.25; b = 0; c = -400;
Δ = b2-4ac
Δ = 02-4·0.25·(-400)
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-20}{2*0.25}=\frac{-20}{0.5}
=-40
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+20}{2*0.25}=\frac{20}{0.5}
=40
$