Full width half maximum - cosine

At http://mathworld.wolfram.com/FullWidthatHalfMaximum.html
there is a list of equations for the FWHM of different functions. For cosine, it’s
FWHM of cos(pix / 2a) = (4/3)a
Given that cos goes from -1 to 1 and 0 is halfway between those, why wouldn’t the FWHM be from 0 to 0, ie 2*a?

Oh right, they’re doing FWHM from 0 to 1 :sweat_smile:

Thanks for the question and the answer :wink: