Cut a single polygon

Hi there, I am trying to cut a single polygon from corner to corner, at a diagonal. I know i can convert this poly to triangles, then spin the edge until it gets to where i want, but why cant i just use the knife subdivide tool to do this?!:no: Is there another hidden tool i should be using?

Ctrl-T will split the quad into tris on one angle. Ctrl-Shift-T will split the quad on the other angle. So one of those two options should give you the split you need.