x^2-0.28*x-0.18*0.18=0

Solution for x^2-0.28*x-0.18*0.18=0 equation:

x^2-0.28x-0.18*0.18=0

We add all the numbers together, and all the variables

x^2-0.28x-0.0324=0

a = 1; b = -0.28; c = -0.0324;
Δ = b2-4ac
Δ = -0.282-4·1·(-0.0324)
Δ = 0.208
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{-(-0.28)-\sqrt{0.208}}{2*1}=\frac{0.28-\sqrt{0.208}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-0.28)+\sqrt{0.208}}{2*1}=\frac{0.28+\sqrt{0.208}}{2}
$