Problem understanding half wave symmetry I am trying to understand half wave symmetry.

I understand the first (a) graphical image is half wave symmetry but (b) seems like even symmetry and (c) seems to be odd symmetry. I am unable to find the difference. Please guide.
Edit: I read my question and it seems to be confusing. I know the b is even symmetry and c is odd but how are they half wave symmetry?

You seem to be assuming that it is an either/or situation. It isn't.  A wave can be all three: odd (OR even), have half wave symmetry, and also have quarter wave symmetry. All your examples have half wave symmetry,  (b) is even in addition to having half wave symmetry, while (c) is odd in addition to having half wave symmetry.
