(0.4-2x)(0.4-2x)=0

Solution for (0.4-2x)(0.4-2x)=0 equation:

(0.4-2x)(0.4-2x)=0

We add all the numbers together, and all the variables

(-2x+0.4)(-2x+0.4)=0

We multiply parentheses ..

(+4x^2-0.8x-0.8x+0.16)=0

We get rid of parentheses

4x^2-0.8x-0.8x+0.16=0

We add all the numbers together, and all the variables

4x^2-1.6x+0.16=0

a = 4; b = -1.6; c = +0.16;
Δ = b2-4ac
Δ = -1.62-4·4·0.16
Δ = 4.4408920985006E-16
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1.6)-\sqrt{4.4408920985006E-16}}{2*4}=\frac{1.6-\sqrt{4.4408920985006E-16}}{8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1.6)+\sqrt{4.4408920985006E-16}}{2*4}=\frac{1.6+\sqrt{4.4408920985006E-16}}{8}
$