Only those that go in frames. The angle is applied while using proper cutting technique for knives. A flat blade would also go dull rather quickly, as only one

Only those that go in frames. The angle is applied while using proper cutting technique for knives. A flat blade would also go dull rather quickly, as only one portion of the blade would be doing all the cutting (well, tearing, a straight drop with a flat blade would be like trying to chop a tomato rather than slicing it).