x^2+x=20.8

Solution for x^2+x=20.8 equation:

x^2+x=20.8

We move all terms to the left:

x^2+x-(20.8)=0

We add all the numbers together, and all the variables

x^2+x-20.8=0

a = 1; b = 1; c = -20.8;
Δ = b2-4ac
Δ = 12-4·1·(-20.8)
Δ = 84.2
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{-(1)-\sqrt{84.2}}{2*1}=\frac{-1-\sqrt{84.2}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{84.2}}{2*1}=\frac{-1+\sqrt{84.2}}{2}
$