A linear function adds the same amount each step. An exponential function multiplies by the same factor each step, like a strip of paper that doubles its layers with every fold. The rules of exponents extend to fractions: 8 to the 1/3 is the cube root of 8, because cubing it must give 8. A percent change hides in a factor (1.05 grows 5%, 0.8 shrinks 20%), and an exponential eventually passes any linear or quadratic function.