1. The problem statement, all variables and given/known data C is a positively orientated simple closed curve Show that the the following integral is always positive. [itex]\int P dx + Q dy[/itex] 2. Relevant equations 3. The attempt at a solution I am actually given a particular P and Q, but I would just like a hint on how to proceed. The integral is presented in such a way that I am tempted to use Green's Theorem, but I'm not sure if that would make it any better. Basically, I am able to show it no problem if I pick particular curves C, and parameterize them. Can anyone give me a hint as to how to do this in the general case when I don't know C exactly.