(X+0.4)(x+1.4)=0

Solution for (X+0.4)(x+1.4)=0 equation:

(X+0.4)(X+1.4)=0

We multiply parentheses ..

(+X^2+1.4X+0.4X+0.56)=0

We get rid of parentheses

X^2+1.4X+0.4X+0.56=0

We add all the numbers together, and all the variables

X^2+1.8X+0.56=0

a = 1; b = 1.8; c = +0.56;
Δ = b2-4ac
Δ = 1.82-4·1·0.56
Δ = 1
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1}=1$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(1.8)-1}{2*1}=\frac{-2.8}{2}
=-1+0.8/2
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1.8)+1}{2*1}=\frac{-0.8}{2}
=-0.8/2
$