Linear models
Commonly seen in the form y = f(x) = mx + c where m represents the gradient/rate of change of the function and c is the y-intercept, where x = 0. These models are a fundamental bit of algebra that come up again and again. they are also fairly commonly used models. For example an electricity bill often has a standing charge that you pay even before you have used any electricity (this is the y - intercept, because...