F(x)=6x^2-900=x

Solution for F(x)=6x^2-900=x equation:

(F)=6F^2-900=F

We move all terms to the left:

(F)-(6F^2-900)=0

We get rid of parentheses

-6F^2+F+900=0

a = -6; b = 1; c = +900;
Δ = b2-4ac
Δ = 12-4·(-6)·900
Δ = 21601
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{21601}}{2*-6}=\frac{-1-\sqrt{21601}}{-12}
$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{21601}}{2*-6}=\frac{-1+\sqrt{21601}}{-12}
$