1,25=x^2+2x

Solution for 1,25=x^2+2x equation:

1.25=x^2+2x

We move all terms to the left:

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

We get rid of parentheses

-x^2-2x+1.25=0

We add all the numbers together, and all the variables

-1x^2-2x+1.25=0

a = -1; b = -2; c = +1.25;
Δ = b2-4ac
Δ = -22-4·(-1)·1.25
Δ = 9
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{9}=3$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-3}{2*-1}=\frac{-1}{-2}
=1/2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+3}{2*-1}=\frac{5}{-2}
=-2+1/2
$