F(-1)=-x^2+x

Solution for F(-1)=-x^2+x equation:

(-1)=-F^2+F

We move all terms to the left:

(-1)-(-F^2+F)=0

We add all the numbers together, and all the variables

-(-F^2+F)-1=0

We get rid of parentheses

F^2-F-1=0

We add all the numbers together, and all the variables

F^2-1F-1=0

a = 1; b = -1; c = -1;
Δ = b2-4ac
Δ = -12-4·1·(-1)
Δ = 5
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$F_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$F_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-\sqrt{5}}{2*1}=\frac{1-\sqrt{5}}{2}
$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+\sqrt{5}}{2*1}=\frac{1+\sqrt{5}}{2}
$