5-9
Problem 3: For each of the following equations, assume a product solution (xy=XxYy) and (where possible) carry out separation of variables to find ordinary differential equations for Xx and Yy. Be sure to distinguish clearly between x and X, y and Y.
1. yux=uyy
2. uxx+4uyy=0
3. uxx+uyy+4u=0
4. uxx+uyy+xu=0
5. uxx+xuyy+xu=0
6. uxx+xyyy=0
7. uxx+(x+2uyy=0
8. uxr+x+yuy=0
9. ax^3+3=0