Is x>y?

i) ax > ay => ax-ay > 0, a(x-y) > 0 posiible if a and (x-y) have the same +ve or -ve sign.
a may be -2 and x-y may be 5-7 = -2 but a(x-y) = +4

ii) a^2 x > a^2 y => a²(x-y) > 0 logic similar to (i) but a² will be +ve for real numbers and (x-y) > 0
The eq holds for any real nos. even if it is not a integer but a fraction.

In the OG11 under the heading 4.3 Problem Solving Sample Questions it is stated that
Numbers : All numbers used are real numbers.
In the Official Guide there is no discussion on complex nos, though real nos are explained.
Anyway, better wait for the experts.

I agree with kstv,

All numbers used are real numbers on GMAT

The unsaid rule : All numbers unless stated are real numbers,,,