2.8+3.1x-0.9x^2=0

Solution for 2.8+3.1x-0.9x^2=0 equation:

2.8+3.1x-0.9x^2=0

a = -0.9; b = 3.1; c = +2.8;
Δ = b2-4ac
Δ = 3.12-4·(-0.9)·2.8
Δ = 19.69
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{-(3.1)-\sqrt{19.69}}{2*-0.9}=\frac{-3.1-\sqrt{19.69}}{-1.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(3.1)+\sqrt{19.69}}{2*-0.9}=\frac{-3.1+\sqrt{19.69}}{-1.8}
$