Question

The notation f:S→T denotes that f is a function, also called a map , defined on all of a set S and whose outputs lie in a set T . A function f:S→T is injective if for all x,y∈S , f(x)=f(y) implies that x=y . Alternatively: a function is injective if we can uniquely recover some input x based on an output f(x) . What functions are injective?

Answer 1

Answer:

There are many. Two examples are

$f(x) = x, \\f(x) = x^3$

Step-by-step explanation:

There are many examples. The simplest is

1 -

$f(x) = x$

It is trivial that

$\text{if \,\,\,\,} f(x) = f(y) \,\,\,\,\,\text{then} \,\,\,\,\, x=y$

2 -

$f(x) = x^3$

That function is injective as well.

$\text{if \,\,\,\,} x^3 = y^3 \,\,\,\,\,\text{then} \,\,\,\,\, x=y$

An example of a function that is NOT injective is

$f(x) = x^2$

Notice that

$f(-2) = (-2)^2 = 2^2 = 4$