Chapter 2.1, Problem 2E

List five elements in each of the following set:

a) $\left\{a+bi|a,b\in Z,i^2=-1\right\}$

b) $\left\{a+b\sqrt{2}|a\in N,-b\in \left\{2,5,7\right\}\right\}$

c) $\left\{\frac{x}{y}|x,y\in R,x^2+y^2=25\right\}$

d) $\left\{n\in N|n^2+n\text{ is a multiple of 3}\right\}$