F(x+3)=4x^2+2x-3

Solution for F(x+3)=4x^2+2x-3 equation:

(F+3)=4F^2+2F-3

We move all terms to the left:

(F+3)-(4F^2+2F-3)=0

We get rid of parentheses

-4F^2+F-2F+3+3=0

We add all the numbers together, and all the variables

-4F^2-1F+6=0

a = -4; b = -1; c = +6;
Δ = b2-4ac
Δ = -12-4·(-4)·6
Δ = 97
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{97}}{2*-4}=\frac{1-\sqrt{97}}{-8}
$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+\sqrt{97}}{2*-4}=\frac{1+\sqrt{97}}{-8}
$