(x+0.5)(x+3.9)=0

Solution for (x+0.5)(x+3.9)=0 equation:

(x+0.5)(x+3.9)=0

We multiply parentheses ..

(+x^2+3.9x+0.5x+1.95)=0

We get rid of parentheses

x^2+3.9x+0.5x+1.95=0

We add all the numbers together, and all the variables

x^2+4.4x+1.95=0

a = 1; b = 4.4; c = +1.95;
Δ = b2-4ac
Δ = 4.42-4·1·1.95
Δ = 11.56
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{-(4.4)-\sqrt{11.56}}{2*1}=\frac{-4.4-\sqrt{11.56}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(4.4)+\sqrt{11.56}}{2*1}=\frac{-4.4+\sqrt{11.56}}{2}
$