So...

  If it can be proved that it can't be proved that two plus two
  is five, then it can be proved as well that two plus two is
  five, and math is a lot of bunk.

Then:

  p: it can't be proved that 2 + 2 = 5
  q: it can be proved that it can't be proved that 2 + 2 = 5

  q → ¬p

Thus if it can be proved that it can't be proved that 2 + 2 = 5 then it can be proved that 2 + 2 = 5. (i.e. when q is true, p cannot be true)

Sorry, had to do this for myself because I'm just starting a course in discrete mathematics!