(0.8-x)(0.9-x)=0

Solution for (0.8-x)(0.9-x)=0 equation:

(0.8-x)(0.9-x)=0

We add all the numbers together, and all the variables

(-1x+0.8)(-1x+0.9)=0

We multiply parentheses ..

(+x^2-0.9x-0.8x+0.72)=0

We get rid of parentheses

x^2-0.9x-0.8x+0.72=0

We add all the numbers together, and all the variables

x^2-1.7x+0.72=0

a = 1; b = -1.7; c = +0.72;
Δ = b2-4ac
Δ = -1.72-4·1·0.72
Δ = 0.01
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{-(-1.7)-\sqrt{0.01}}{2*1}=\frac{1.7-\sqrt{0.01}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1.7)+\sqrt{0.01}}{2*1}=\frac{1.7+\sqrt{0.01}}{2}
$