F(x)=15x^2+9x

Solution for F(x)=15x^2+9x equation:

(F)=15F^2+9F

We move all terms to the left:

(F)-(15F^2+9F)=0

We get rid of parentheses

-15F^2+F-9F=0

We add all the numbers together, and all the variables

-15F^2-8F=0

a = -15; b = -8; c = 0;
Δ = b2-4ac
Δ = -82-4·(-15)·0
Δ = 64
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$F_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{64}=8$
$F_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-8}{2*-15}=\frac{0}{-30}
=0
$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+8}{2*-15}=\frac{16}{-30}
=-8/15
$