Hi all,

I am given two relations and asked to prove which one is an equivilence relation for integers.

They are;

$\displaystyle x$~$\displaystyle _{1}y$ if $\displaystyle x^{2}+y^{2}$ is divisible by 5.

$\displaystyle x$~$\displaystyle _{2}y$ if $\displaystyle x^{2}-y^{2}$ is divisible by 4.

The problem i'm having is finding which one has reflexivity.

for example, $\displaystyle 1^{2}+1^{2}=2$ which is not divisble by 5.

and, $\displaystyle k^{2}-k^{2}=0$ for all $\displaystyle k$

So, is zero divisible by 4?