(f-8)(2f+9)=0

Solution for (f-8)(2f+9)=0 equation:

(f-8)(2f+9)=0

We multiply parentheses ..

(+2f^2+9f-16f-72)=0

We get rid of parentheses

2f^2+9f-16f-72=0

We add all the numbers together, and all the variables

2f^2-7f-72=0

a = 2; b = -7; c = -72;
Δ = b2-4ac
Δ = -72-4·2·(-72)
Δ = 625
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{625}=25$
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-25}{2*2}=\frac{-18}{4}
=-4+1/2
$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+25}{2*2}=\frac{32}{4}
=8
$