When the original frequency increases past the sampling frequency, the aliased frequency also switches directions and starts increasing as well.
You might be able to notice that the phase of the signal also changes at this point.
So:
\fo = {7.50} = \fnv{5.00} + {2.50}
becomes:
\fav{2.50} = {2.50} = \fnv{5.00} - {2.50}