8-5 Linear, Exponential, and Quadratic Models – We learned to determine which model: linear, exponential, or quadratic would best fit a set of data. Then we used fitted functions to solve problems in the context of data. Linear, quadratic, and exponential functions are differentiated by their average rates of change over different intervals. A linear function models a relationship between x and y in which the differences between successive y-values are constant. A quadratic function models a relationship in which the second differences, or the difference between the first differences, are constant. An exponential function models a relationship where the ratios of consecutive y-values are constant. Review for Test on Topic 8 Quadratic Functions.