Zill, D. G., Wright, W. S., & Cullen, . M. R. (2013). Differential equations with boundary-value problems (Eight edition.). Brooks/Cole Cengage Learning.

Zill, Dennis G., Warren S. Wright, and Michael R. Cullen. Differential Equations with Boundary-value Problems. Eight edition. Australia: Brooks/Cole Cengage Learning, 2013.

Zill, Dennis G., et al. Differential Equations with Boundary-value Problems. Eight edition. Brooks/Cole Cengage Learning, 2013.