1.8+0.4x-0.002x^2=0

Solution for 1.8+0.4x-0.002x^2=0 equation:

1.8+0.4x-0.002x^2=0

a = -0.002; b = 0.4; c = +1.8;
Δ = b2-4ac
Δ = 0.42-4·(-0.002)·1.8
Δ = 0.1744
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{-(0.4)-\sqrt{0.1744}}{2*-0.002}=\frac{-0.4-\sqrt{0.1744}}{-0.004}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0.4)+\sqrt{0.1744}}{2*-0.002}=\frac{-0.4+\sqrt{0.1744}}{-0.004}
$