When I’ve taught Calculus III, Green’s Theorem was the last thing we covered.
Why do you want to begin studying Calculus III?
Do you just really like math and want to learn more? Are you trying to prep for college classes? What’s the point/goal?
There are a few reasons, the biggest being I want to become a physicist and I like math. I would also like a small head-start for my future classes.
We touched on Green’s functions in our second year calculus class in high school after having already been exposed via our 2nd year (multivariable calculus based) physics class, though we didn’t go into rigorous detail on it.
Another reason “Calculus III” isn’t descriptive by itself.
Greens theorem is useful to help derive field strengths,field flux in the electric, magnetic, etc fields … Useful for those perpendicular situations… electricity this way, magnetic field around that way. define a perimeter , where its all the same strength, and then you get the flux through that perimeter… much easier than integrating the varying strengths through perimeter, you’ve done it by considering the perimeter only. Basically given to you as those laws named for physicists…
So that might be why its mentioned in in calculus for physics, earlier than its derivation in multivariable calculus.
In those cases Green’s theorem, Stokes’s theorem, Green’s functions, the heat kernel, etc. are being taught in the calculus-for-physicists class probably as a prerequisite for certain physics courses, so one would have to examine the syllabi for those and not only the mathematics courses to see what is required.