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

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

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

We multiply parentheses ..

(+8u^2-64u+9u-72)=0

We get rid of parentheses

8u^2-64u+9u-72=0

We add all the numbers together, and all the variables

8u^2-55u-72=0

a = 8; b = -55; c = -72;
Δ = b2-4ac
Δ = -552-4·8·(-72)
Δ = 5329
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{5329}=73$
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-55)-73}{2*8}=\frac{-18}{16}
=-1+1/8
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-55)+73}{2*8}=\frac{128}{16}
=8
$