F(-2)=x^2-17

Solution for F(-2)=x^2-17 equation:

(-2)=F^2-17

We move all terms to the left:

(-2)-(F^2-17)=0

We add all the numbers together, and all the variables

-(F^2-17)-2=0

We get rid of parentheses

-F^2+17-2=0

We add all the numbers together, and all the variables

-1F^2+15=0

a = -1; b = 0; c = +15;
Δ = b2-4ac
Δ = 02-4·(-1)·15
Δ = 60
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:

$\sqrt{\Delta}=\sqrt{60}=\sqrt{4*15}=\sqrt{4}*\sqrt{15}=2\sqrt{15}$
$F_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{15}}{2*-1}=\frac{0-2\sqrt{15}}{-2}
=-\frac{2\sqrt{15}}{-2}
=-\frac{\sqrt{15}}{-1}
$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{15}}{2*-1}=\frac{0+2\sqrt{15}}{-2}
=\frac{2\sqrt{15}}{-2}
=\frac{\sqrt{15}}{-1}
$