F(2x)=8-4x^2

Solution for F(2x)=8-4x^2 equation:

(2F)=8-4F^2

We move all terms to the left:

(2F)-(8-4F^2)=0

We get rid of parentheses

4F^2+2F-8=0

a = 4; b = 2; c = -8;
Δ = b2-4ac
Δ = 22-4·4·(-8)
Δ = 132
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$F_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{132}=\sqrt{4*33}=\sqrt{4}*\sqrt{33}=2\sqrt{33}$
$F_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-2\sqrt{33}}{2*4}=\frac{-2-2\sqrt{33}}{8}
$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+2\sqrt{33}}{2*4}=\frac{-2+2\sqrt{33}}{8}
$