I'm doing a practice exam for a math test on thursday, wondering if anyone could help figure out how to get from one step to the next. i dont think that the background info is necessary for these two steps.(adsbygoogle = window.adsbygoogle || []).push({});

the file is attached (Adobe acrobat).

what i am wondering about is the answer under (2b).

If the solution for finding (del)u(x,y) were lettered a through d (4 steps, i am wondering how the professer got from b to c.

of course i have emailed him as well.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Periodic functions

**Physics Forums | Science Articles, Homework Help, Discussion**