F(x)=2.5x^2+10x-15

Solution for F(x)=2.5x^2+10x-15 equation:

(F)=2.5F^2+10F-15

We move all terms to the left:

(F)-(2.5F^2+10F-15)=0

We get rid of parentheses

-2.5F^2+F-10F+15=0

We add all the numbers together, and all the variables

-2.5F^2-9F+15=0

a = -2.5; b = -9; c = +15;
Δ = b2-4ac
Δ = -92-4·(-2.5)·15
Δ = 231
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{-(-9)-\sqrt{231}}{2*-2.5}=\frac{9-\sqrt{231}}{-5}
$
$F_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-9)+\sqrt{231}}{2*-2.5}=\frac{9+\sqrt{231}}{-5}
$