Finney, R. L., Giordano, F. R., Weir, M. D., Thomas, G. B., Jr., & Calculus and analytic geometry. (2001). Thomas’ calculus (Tenth edition / based on the original work by George B. Thomas, Jr.,as revised by Ross L. Finney, Maurice D. Weir, and Frank R. Giordano.). Addison-Wesley.
Average rate of change of function $y=f(x)$ is given by $\frac{\Delta y}{\Delta y}$
For limit of function we have,
