F(x)=-7x^2+5x

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

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

We move all terms to the left:

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

We get rid of parentheses

7F^2-5F+F=0

We add all the numbers together, and all the variables

7F^2-4F=0

a = 7; b = -4; c = 0;
Δ = b2-4ac
Δ = -42-4·7·0
Δ = 16
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$F_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{16}=4$
$F_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4)-4}{2*7}=\frac{0}{14}
=0
$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4)+4}{2*7}=\frac{8}{14}
=4/7
$