(X+0.9)(x+1.9)=0

Solution for (X+0.9)(x+1.9)=0 equation:

(X+0.9)(X+1.9)=0

We multiply parentheses ..

(+X^2+1.9X+0.9X+1.71)=0

We get rid of parentheses

X^2+1.9X+0.9X+1.71=0

We add all the numbers together, and all the variables

X^2+2.8X+1.71=0

a = 1; b = 2.8; c = +1.71;
Δ = b2-4ac
Δ = 2.82-4·1·1.71
Δ = 1
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{-(2.8)-\sqrt{1}}{2*1}=\frac{-2.8-\sqrt{1}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2.8)+\sqrt{1}}{2*1}=\frac{-2.8+\sqrt{1}}{2}
$