Question

Give an example of a relation that is a function and explain why it is a function.

Answer 1

f(x) = 2x is a function. A function by definition has a unique value for each unique value of the input. In this case, for every different value of x, you get one and only one value of f(x) - function value.

Answer 2

You can see GT's answer visually by graphing the relation and drawing a vertical line through it. If the vertical line intersects the graph of the relation only once, it is a function.