Are transformations of functions giving your students trouble? Try a covariation approach.
Consider this problem: Sketch a graph of a function y=f(x). Now sketch a graph of y=f(ax) for some constant value a>1. Reflect. What kind of graph did you sketch for y=f(x)? How did you decide what to sketch? Did you choose a particular value for a? How does your graph of y=f(ax) compare to your graph of y=f(x)? What is …
