Hi all, I have an answer which is puzzeling me

from the answer page it reads;

ifLis the length of the shorter edge, by pythag` theorem, 2L^2 =a^2, so L^2=1/2a^2

Hence the shorter edge L, has length a/sqrt 2

if it helps the picture is a right angled triangle with a hyp` of length given asa, and the two shorter lenghts given asL

what I can`t get is why the shorter edge L, has length a/sqrt 2

Dave