Classify `f: N->N` given by `f(x)=x^2` as injection, surjection or bijection.

Explanation

Injection condition:

Let `x` and `y` be any two elements in domain `(N)`, such that `f(x) = f(y)`.

`f(x) = f(y)`

`x^2 = y^2=> x = y` (We do not get `pm` because `x` and `y` are in `N` that is natural numbers)

So, `f` is an injection.

Surjection condition:

Let `y` be any element in the co-domain `(N)`, such that `f(x) = y` for some element `x` in `N` (domain).

`f(x) = y`
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