X^2-0.4x-1.2=0

Solution for X^2-0.4x-1.2=0 equation:

X^2-0.4X-1.2=0

a = 1; b = -0.4; c = -1.2;
Δ = b2-4ac
Δ = -0.42-4·1·(-1.2)
Δ = 4.96
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{-(-0.4)-\sqrt{4.96}}{2*1}=\frac{0.4-\sqrt{4.96}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-0.4)+\sqrt{4.96}}{2*1}=\frac{0.4+\sqrt{4.96}}{2}
$