Copyright © 2009 Rong Cheng and Dongfeng Zhang. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
We first prove a generalized Wirtinger's inequality. Then, applying the inequality, we study estimates for lower bounds of periods of periodic solutions for a class of delay differential equations , and , where , , and and , are two given constants. Under some suitable conditions on and , lower bounds of periods of periodic solutions for the equations aforementioned are obtained.