0.4x^2+7.2x=-1

Solution for 0.4x^2+7.2x=-1 equation:

0.4x^2+7.2x=-1

We move all terms to the left:

0.4x^2+7.2x-(-1)=0

We add all the numbers together, and all the variables

0.4x^2+7.2x+1=0

a = 0.4; b = 7.2; c = +1;
Δ = b2-4ac
Δ = 7.22-4·0.4·1
Δ = 50.24
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{-(7.2)-\sqrt{50.24}}{2*0.4}=\frac{-7.2-\sqrt{50.24}}{0.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(7.2)+\sqrt{50.24}}{2*0.4}=\frac{-7.2+\sqrt{50.24}}{0.8}
$