Students will learn how to identify intervals of functions which are invertible. This is a direct application of the horizontal line test. Here's a lesson, and here's practice.

Conclude by giving your students these challenges:

- 2020 Math Kangaroo Levels 5-6 Problem #22 by STEM4all
- Multiple Surprises by NRICH
- Is it Magic or Is it Maths? by NRICH
- Olympic Records by NRICH
- Divisible by 13