Education Technology

Mathematics lessons for IB® Diploma Programme

Applications and Interpretation | Functions

Function, or Not a Function?

Activity Overview

In this lesson, students are presented with graphs and tables and asked to determine which represent functions and which do not. A function associates exactly one output value y with each possible input value x. If more than one output value y is associated with a single input value x, that process does not describe a function.


  • Students will understand the definition of function and use it to identify whether or not an input-output pairing represents a function.
  • Students will determine if a graph represents a function by using a moving vertical line.
  • Students will determine if a table of x- and y-values represents a function.


  • function