(3u+8)(9+u)=0

Solution for (3u+8)(9+u)=0 equation:

(3u+8)(9+u)=0

We add all the numbers together, and all the variables

(3u+8)(u+9)=0

We multiply parentheses ..

(+3u^2+27u+8u+72)=0

We get rid of parentheses

3u^2+27u+8u+72=0

We add all the numbers together, and all the variables

3u^2+35u+72=0

a = 3; b = 35; c = +72;
Δ = b2-4ac
Δ = 352-4·3·72
Δ = 361
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{361}=19$
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(35)-19}{2*3}=\frac{-54}{6}
=-9
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(35)+19}{2*3}=\frac{-16}{6}
=-2+2/3
$