Question

Is `x^2=y+1` a function?

Answer 1

The formal Definition of a Function is

"A function relates each element of a set with exactly one element of another set"

Hence for `y=x^2-1` it is a function.

Answer 2

In support of Constantinos contribution: Pick any 1 value for `x`. If that 1 value of `x` relates to only 1 value of `y` then it is a function.