-0,2x2+2,1x+4,2=0

Solution for -0,2x2+2,1x+4,2=0 equation:

-0.2x^2+2.1x+4.2=0

a = -0.2; b = 2.1; c = +4.2;
Δ = b2-4ac
Δ = 2.12-4·(-0.2)·4.2
Δ = 7.77
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{-(2.1)-\sqrt{7.77}}{2*-0.2}=\frac{-2.1-\sqrt{7.77}}{-0.4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2.1)+\sqrt{7.77}}{2*-0.2}=\frac{-2.1+\sqrt{7.77}}{-0.4}
$