1.2=x-0.1x^2

Solution for 1.2=x-0.1x^2 equation:

1.2=x-0.1x^2

We move all terms to the left:

1.2-(x-0.1x^2)=0

We get rid of parentheses

0.1x^2-x+1.2=0

We add all the numbers together, and all the variables

0.1x^2-1x+1.2=0

a = 0.1; b = -1; c = +1.2;
Δ = b2-4ac
Δ = -12-4·0.1·1.2
Δ = 0.52
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)-\sqrt{0.52}}{2*0.1}=\frac{1-\sqrt{0.52}}{0.2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+\sqrt{0.52}}{2*0.1}=\frac{1+\sqrt{0.52}}{0.2}
$