The relation R={(x,y):x,y\in Z and x+y is even } is:
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Official solution
R={(x,y):x,y∈z and x+y is even }
reflexive x+x=2x even
symmetric of x+y is even, then (y+x) is also even
transitive of x+y is even &y+z is even then x+z is also even
So, relation is an equivalence relation.