Let's do it this way.....let x= n^2
Substitute:
x^2 -11x+30 / x^2-7x+10 factor top and bottom
(x-6)(x-5) / (x-2)(x-5) Now put the n's back in
(n^-6)(n^2-5) / (n^2-2)(n^2-5) Now you can see that n^2 cannot equal 2 or 5
so n cannot equal +-sqrt2 or +- sqrt 5
cancel out the (n^2-5) in num and denom
(n^2-6) / (n^2-2)