Let's begin by listing out the given information:
I.
II.
A function assigns one element of x in a set A to exactly one element called f(x) in a set B
The first function
Every element of x has a distinct element in y.
the second function
The element x = 1, has 2 different elements in y. We see y has 2 different values from the same value of x
Therefore, the first function defines y as a function of x