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

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

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

We move all terms to the left:

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

We add all the numbers together, and all the variables

-((-1x+0.4)(-1x+0.4))+0=0

We add all the numbers together, and all the variables

-((-1x+0.4)(-1x+0.4))=0

We multiply parentheses ..

-((+x^2-0.4x-0.4x+0.16))=0


We calculate terms in parentheses: -((+x^2-0.4x-0.4x+0.16)), so:

(+x^2-0.4x-0.4x+0.16)

We get rid of parentheses

x^2-0.4x-0.4x+0.16

We add all the numbers together, and all the variables

x^2-0.8x+0.16

Back to the equation:

-(x^2-0.8x+0.16)


We get rid of parentheses

-x^2+0.8x-0.16=0

We add all the numbers together, and all the variables

-1x^2+0.8x-0.16=0

a = -1; b = 0.8; c = -0.16;
Δ = b2-4ac
Δ = 0.82-4·(-1)·(-0.16)
Δ = 1.1102230246252E-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{-(0.8)-\sqrt{1.1102230246252E-16}}{2*-1}=\frac{-0.8-\sqrt{1.1102230246252E-16}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0.8)+\sqrt{1.1102230246252E-16}}{2*-1}=\frac{-0.8+\sqrt{1.1102230246252E-16}}{-2}
$