Physics hw help, i'm having a bit of trouble conservative forces

[MarineTeng]

i don't really understand out to tell if it's a conservative force from just looking at an equation, here's is one of my problems
which of the following forces is not conservative?
A F= 3i + 4j
B F = 3xi + 4yj
C F = 3yi + 4xj
D F = 3x^2i + 4y^2j
this is all with f being a force vector and i and j being unit vectors, thanks, i really have more questions but figured i'd start with this one thanks a bunch

 

[Slickdonkey]

Probably too late to help you but if I recall my physics correctly there are several ways to figure this out, but the easiest way would be to compute the curl of the vector field. If it's equal to zero then it is a conservative force.

 

[MarineTeng]

ya, the final for the class is over, thanks though,