I attached a screen shot of my notebook. I'm using the DSolve function for a few simple diff eq to familiarize myself with the software. The first equation I entered worked fine. For some reason any other diff eqs I try to solve in the same notebook won't work. I tried changing the assignment of variables to (t,u) instead of (x,y) for the second diff eq to see if it had anything to do with previous use of (x,y) in the first equation. It still didn't work. What am I missing here?