By (x + 5/x^2 + 9x + 20) you apparently meant the following:
x+5
----------------------
x^2 + 9x + 20
and by
(x^2-16/x-4)
x^2-16
you apparently meant ---------------
x - 4
Please use additional parentheses for clarity.
Dividing,
x+5 (x-4)(x+4)
---------------------- * ---------------
x^2 + 9x + 20 x-4
Now, x^2 + 9x + 20 factors into (x+4)(x+5), so what we have now is
(x+5)(x+4)
------------------------- = 1 This is true for all x, so there are no exclusions.
(x+4)(x+5)
