(9u-7)(9u+1)=0

Solution for (9u-7)(9u+1)=0 equation:

(9u-7)(9u+1)=0

We multiply parentheses ..

(+81u^2+9u-63u-7)=0

We get rid of parentheses

81u^2+9u-63u-7=0

We add all the numbers together, and all the variables

81u^2-54u-7=0

a = 81; b = -54; c = -7;
Δ = b2-4ac
Δ = -542-4·81·(-7)
Δ = 5184
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{5184}=72$
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-54)-72}{2*81}=\frac{-18}{162}
=-1/9
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-54)+72}{2*81}=\frac{126}{162}
=7/9
$