when it comes to sets first what I would do is draw three intersecting cirlces that represent the sets then test your hypothesis...that is the best way to visualize...from there it may become readily apparent how to do the problem
And to prove that two sets are equal, you prove that they are subsets of each other - not "because (x,y) is on both (A\B)xC and (AxC)\(BxC)" but maybe that's what you mean.
OK I'm giving it a try... not sure if this makes sense:
So for the second part...
If (x,y) is in [(AxC)\(BxC)] then (x,y) is not in (BxC).
This means that x is not in B or y is not in C.
Since (x,y) is in (AxC) then y is in C, so x is not in B.
Therefore, x is in A, x is not in B, and y is in C,
so (x,y) is in (A\B) x C.
Therefore [(AxC)\(BxC)] is a subset of (A\B)xC (and from before vice versa), so the two sides are equal.
Does this make sense at all??