R,f(x)≤1R, f(x) \leq 1R,f(x)≤1
R−{3},R−{6}R-\{3\}, R-\{6\}R−{3},R−{6}
R,−2≤f(x)≤2R,-2 \leq f(x) \leq 2R,−2≤f(x)≤2
R−{2},R−{0}R-\{2\}, R-\{0\}R−{2},R−{0}
