F(x)=7-5x^2

Solution for F(x)=7-5x^2 equation:

(F)=7-5F^2

We move all terms to the left:

(F)-(7-5F^2)=0

We get rid of parentheses

5F^2+F-7=0

a = 5; b = 1; c = -7;
Δ = b2-4ac
Δ = 12-4·5·(-7)
Δ = 141
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{141}}{2*5}=\frac{-1-\sqrt{141}}{10}
$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{141}}{2*5}=\frac{-1+\sqrt{141}}{10}
$