-0.1x^2+0.21x=0

Solution for -0.1x^2+0.21x=0 equation:

-0.1x^2+0.21x=0

a = -0.1; b = 0.21; c = 0;
Δ = b2-4ac
Δ = 0.212-4·(-0.1)·0
Δ = 0.0441
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{-(0.21)-\sqrt{0.0441}}{2*-0.1}=\frac{-0.21-\sqrt{0.0441}}{-0.2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0.21)+\sqrt{0.0441}}{2*-0.1}=\frac{-0.21+\sqrt{0.0441}}{-0.2}
$