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

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

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

We add all the numbers together, and all the variables

(2u+9)(-1u+8)=0

We multiply parentheses ..

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

We get rid of parentheses

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

We add all the numbers together, and all the variables

-2u^2+7u+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:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

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