F(x)=5x^2-15x

Solution for F(x)=5x^2-15x equation:

(F)=5F^2-15F

We move all terms to the left:

(F)-(5F^2-15F)=0

We get rid of parentheses

-5F^2+F+15F=0

We add all the numbers together, and all the variables

-5F^2+16F=0

a = -5; b = 16; c = 0;
Δ = b2-4ac
Δ = 162-4·(-5)·0
Δ = 256
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$F_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{256}=16$
$F_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(16)-16}{2*-5}=\frac{-32}{-10}
=3+1/5
$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(16)+16}{2*-5}=\frac{0}{-10}
=0
$