REFERENCES
- Howard Anton, Calculus with Analytic Geometry (2nd ed.), John Wiley and Sons, 1984.
- D. J. Foulis and M. A. Munem, Calculus with Analytic Geometry (2nd ed.), Worth Publishing Inc., 1984.
- John B. Fraleigh, Calculus with Analytic Geometry, Addison-Wesley, 1981.
- Philip Gillett, Calculus and Analytic Geometry (2nd ed.), D. C. Heath and Company, 1984.
- Edwin Purcell and Dale Varberg, Calculus with Analytic Geometry (4th ed.), Prentice-Hall, 1984.
- E. L. Roetman, “Tangent Planes and Differentiation,” Mathematics Magazine 43 (Jan. 1970) 1–7.
- H. Thurston, “Tangents: An Elementary Survey.” Mathematics Magazine 42 (Jan. 1969) 1–11.
- H. Thurston, “On the Definition of the Tangent Line,” American Mathematical Monthly 71 (December 1964) 1099–1103.