Official solution
Given R = {(x, y) : x, y
\[ \in \] Z, x2 + 3y2
\[ \le \] 8}
So R = {(0,1), (0,--1), (1,0), (--1,0), (1,1), (1,-1)
(-1,1), (-1,-1), (2,0), (-2,0), (-2,0), (2,1), (2,-1), (-2,1), (-2,-1)}
\[ \Rightarrow \] R : { -2, -1, 0, 1, 2} \[ \to \] {-1, 0, 1}
\[ \therefore \] R-1 : {-1, 0, 1} \[ \to \] { -2, -1, 0, 1, 2}
\[ \therefore \] Domain of R--1 = {-1, 0, 1}