Here's the question you clicked on:
Alfonso92
Show that the given integral represent the indicated function. The integral tells you wich one, and its value tells you what function to consider. (Show the detalis of you works)
The instructions hint for you to "use (5), (11), or (13)". What does does this mean? Also, this doesn't look like anything out of Differential Equations, and instead looks like something out of Fourier Series--perhaps you should start a study group on the topic.