作CH⊥AB,H为垂足,
根据勾股定理得,
AB=13
CH=AC*BC/AB=60/13,
AH=AC^2/AB=144/13,
作DE⊥AB,
DE‖CH,
DE/CH=AD/AC=(AC-CD)/AC=(12-x)/12,
DE=(12-x)/12*(60/13)=5(12-x)/13,
S△ADM=DE*AM/2=5(12-x)*6/13/2=15(12-x)/13,
S△ABC/S△ADM=(AC*BC/2)/[15(12-x)/13]=30/[15(12-x)/13]=26/(12-x),
∴y=26/(12-x)(0