A function can be any straight line except a line.

vertical line.

Step-by-step explanation:

Ok we can define a function f(x) as "something" that maps a given input (we usually call the input "x") into a given output (we usually call the output "y")

We have one rule for functions, each input can be mapped into only one output.

So if for example, for a given value x = A.

f(A) = B

and

f(A) = C

This is mapping the input A into two different outputs, then this is not a function.

Now to the question.

If we have a vertical line (parallel to the y-axis)

This line will have only one value of x associated with it, but all the values of y.

This means that this maps one value of the input into infinite outputs, then this can not be a function.

a

explanation: