http://i54.tinypic.com/1z2q1dl.png
for the first question, can i assume the non-empty set A has more than one element, and say a = something and b = something to give example.
http://i54.tinypic.com/1z2q1dl.png
for the first question, can i assume the non-empty set A has more than one element, and say a = something and b = something to give example.
No, you can't. Choose for example $\displaystyle A=\{0\}$ . A little help: Reflexive For all $\displaystyle x\in\mathbb{Z}$ we have $\displaystyle x-x=0$ . But $\displaystyle 0\in A$ because being $\displaystyle A\neq \emptyset$ , choosing $\displaystyle a\in A$ we have $\displaystyle a-a=0\in A$ . Conclusion: $\displaystyle xRx$ .
Try the rest.