The numerator and denominator of 1 are close to the limit of 0, and 1 is (x squared +ax+b), and then (x squared +ax+b=(x- 1)(x+b) decomposition factor. . .

If a is not o and a is constant, then lim(a/x) can only be infinite, and infinity is meaningless.

3 limsin(nπ)n is an integer sin(nπ)=0, otherwise there is something wrong with the answer.

I don't understand. I will help you solve it tonight.