Hi All,

Can any one confirm that $\displaystyle \int\frac{1}{x+y}dx=ln(x+y)+C$ since the top is the derivative of the bottom? It is part of my bigger question for solving for u using method of characteristics

$\displaystyle \frac{\partial u}{\partial x}-\frac{\partial u}{\partial y}=\frac{u}{x+y}$

Thanks