General functional notation (e.g. f(x) ) is not supported. If you wish to draw a function such as f(x) = x^2, replace f(x) with y (or any other unused variable).

How do you define the function depends on the conditions given in the problem.

Test different values of x, and determine:
Does every value of x correspond to exactly one value of y? If the answer is yes, then y is a function of x. If the answer is no, then y isn’t a function of x.

You can also graph and see (click here to see the graph). 

If it is not possible to draw a vertical line to touch/intersect the graph in more than one place, then y is a function of x.