Edwards, C. H. 1., Calvis, D., & Penney, D. E. (2009). Elementary differential equations with boundary value problems (6th ed.). Upper Saddle River; London: Pearson Education,.

Edwards, C. Henry 1937-, David Calvis, and David E. Penney. Elementary Differential Equations With Boundary Value Problems. 6th ed. Upper Saddle River; London: Pearson Education,, 2009.

Edwards, C. Henry 1937-, David Calvis, and David E. Penney. Elementary Differential Equations With Boundary Value Problems. 6th ed. Upper Saddle River; London: Pearson Education,, 2009.