F(x)=16-x^2

Solution for F(x)=16-x^2 equation:

(F)=16-F^2

We move all terms to the left:

(F)-(16-F^2)=0

We get rid of parentheses

F^2+F-16=0

a = 1; b = 1; c = -16;
Δ = b2-4ac
Δ = 12-4·1·(-16)
Δ = 65
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{65}}{2*1}=\frac{-1-\sqrt{65}}{2}
$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{65}}{2*1}=\frac{-1+\sqrt{65}}{2}
$