Here, relation R is defined on the set Z.
And by the given definition of relation, R={(x,y) : x,yϵ Z ,x2 +y2=9}
={(-3,0),(0,-3),(3,0),(0,3)}
Now we know,Domain is the set which consist all first elements of ordered pairs in relation R.
So,Domain(R)={-3,0,3}