Question

Is {(1, 2); (1, 3); (1, 4); (1, 5)} a function?

Answer 1

No

Explanation:

To be a function the same value of `x` can not map into multiple values of `y`
Since `(x,y)={(1,2), (1,3), (1,4), (1,5)}`
has `x` (as `1`) mapping into 4 different values,
this can not be a function.