Sobel, M. A., & Lerner, N. (1991). Algebra and trigonometry (4th ed.). Prentice hall.
Cita Chicago (17th ed.)Sobel, Max A., i Norbert Lerner. Algebra and Trigonometry. 4th ed. Englewood cliffs: Prentice hall, 1991.
Cita MLA (9th ed.)Sobel, Max A., i Norbert Lerner. Algebra and Trigonometry. 4th ed. Prentice hall, 1991.
Atenció: Aquestes cites poden no estar 100% correctes.