Tomorrow I have to teach about affine functions ($f(x)=ax+b$) during 20 minutes. I want to know if someone has a suggestion what things I should teach. I want to make this into something interesting, so I'm thinking to beginning with some real world problem, do you have some good example?
Last question, someone knows an article which explains about how to teach affine functions?
I remember that my teacher introduced it by using one to model the side of a hill. The hill was in the shape of a triangle. The premise was that the hill was flattening out, and so we had to calculate the various slopes of the equation of the sloped side of the hill as it flattened. That is probably a good intuitive way to introduce slope, before going into more mathematical and abstract study of a linear function.