Question

8u/u^2-18u+81 subtract 72/u^2-18u+81

Answer 1

Your question is:
$\frac{8u}{u^2-18u+81} -\frac{72}{u^2-18u+81}$
Then, the above formula equate:

$\frac{8u-72}{u^2-18u+81}$
Factor out 8 from the numerator we get:
$\frac{u-9}{u^2-18u+81}$
Factorization of the denominator:
$\frac{u-9}{(u-9)^2}$
Simplifying the numerator and the denominator by (u-9) we get:
$\frac{1}{(u-9)}$