Hi all! Here is my question which I am stuck on:

(its actually in 2 parts)

(a) If $\displaystyle f\rightarrow\mathbb{R}$, with D= { x | x is irrational} and $\displaystyle f(x) =\frac{2x}{x-3}$, evaluate $\displaystyle \lim_{x\to\infty}f(x)$ and prove the result.

(b) If $\displaystyle f:\mathbb{Q}\rightarrow\mathbb{R}$ is defined by $\displaystyle f(x)=\frac{x^2+1}{x-2}$, evaluate $\displaystyle \lim_{x\to-\infty}f(x)$ and prove the result.

What do I do?

Thanks