设CM=x.有BM=1-x.
EM=根号下0.5^2+(1-x)^2
HM=EM-EH=EM-0.5
DH=AD=DC=1
DM=根号下HM^2+DH^2
又DM=根号下x^2+DC^2
所以,(EM-0.5)^2+1=x^2+1
x=1/3