Answer:
[tex]x[/tex] must be number different to 1, 2 and 3 to guarantee that given relation is a function.
Step-by-step explanation:
From Function Theory, we know that a function is a relation in which all domain elements are not related to at least two different elements from range. Which means that [tex]x \in \mathbb{R}-\{1,2,3\}[/tex], that is, that [tex]x[/tex] is a real number different to 1, 2 and 3.
Hence, we conclude that [tex]x[/tex] must be number different to 1, 2 and 3 to guarantee that given relation is a function.