(r+8)(r+9)=0

Solution for (r+8)(r+9)=0 equation:

(r+8)(r+9)=0

We multiply parentheses ..

(+r^2+9r+8r+72)=0

We get rid of parentheses

r^2+9r+8r+72=0

We add all the numbers together, and all the variables

r^2+17r+72=0

a = 1; b = 17; c = +72;
Δ = b2-4ac
Δ = 172-4·1·72
Δ = 1
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1}=1$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(17)-1}{2*1}=\frac{-18}{2}
=-9
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(17)+1}{2*1}=\frac{-16}{2}
=-8
$