We observe the set doesn't have two points with the same x value, so this is a function. Let's look at the answers.
a The set is a function since each element in the domain has a different element in the range.
No, this is more the idea of one-to-one or injectivity.
b The set is a function since each element in the range has a different element in the domain.
This isn't quite right either but we're going to choose it as the best answer. It's not that each element in the range has a different element in the domain; that would be onto aka surjectivity. It's that each element in the set, each point, has a different element in the domain, a different y coordinate. It's ok if two different x coordinates map to the same y coordinate, which they don't here but they could.
Answer: b
c The set is not a function since each element in the domain has a different element in the range.
Nope, it is a function.
d The set is not a function since each element in the range has a different element in the domain.
Nope, it is a function.
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