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

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

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

We multiply parentheses ..

(+4f^2+16f+18f+72)=0

We get rid of parentheses

4f^2+16f+18f+72=0

We add all the numbers together, and all the variables

4f^2+34f+72=0

a = 4; b = 34; c = +72;
Δ = b2-4ac
Δ = 342-4·4·72
Δ = 4
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{4}=2$
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(34)-2}{2*4}=\frac{-36}{8}
=-4+1/2
$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(34)+2}{2*4}=\frac{-32}{8}
=-4
$