Functions and their graphs, after studying this section, you will be able to: understand function notation; apply transformations to the graphs of various functions; Functions. y = f(x) stands for 'y is a function of x' When y = x 2 + 13 then f(x) = x 2 + 13. Therefore from the above f(x) + x = x 2 + 13 + x. Transforming graphs of functions