0=2.5x+2.5x^2

Solution for 0=2.5x+2.5x^2 equation:

0=2.5x+2.5x^2

We move all terms to the left:

0-(2.5x+2.5x^2)=0

We add all the numbers together, and all the variables

-(2.5x+2.5x^2)=0

We get rid of parentheses

-2.5x^2-2.5x=0

a = -2.5; b = -2.5; c = 0;
Δ = b2-4ac
Δ = -2.52-4·(-2.5)·0
Δ = 6.25
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{-(-2.5)-\sqrt{6.25}}{2*-2.5}=\frac{2.5-\sqrt{6.25}}{-5}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2.5)+\sqrt{6.25}}{2*-2.5}=\frac{2.5+\sqrt{6.25}}{-5}
$