-0.4x^2+5.2x+3=0

Solution for -0.4x^2+5.2x+3=0 equation:

-0.4x^2+5.2x+3=0

a = -0.4; b = 5.2; c = +3;
Δ = b2-4ac
Δ = 5.22-4·(-0.4)·3
Δ = 31.84
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{-(5.2)-\sqrt{31.84}}{2*-0.4}=\frac{-5.2-\sqrt{31.84}}{-0.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(5.2)+\sqrt{31.84}}{2*-0.4}=\frac{-5.2+\sqrt{31.84}}{-0.8}
$