DG‖AB,∠CDG=∠A=60度,∠CGD=∠CBA=60度,CD=DG=CG=xDG‖AB,∠E=∠FDG,BE=CD,∠FBE=∠FGD,△此散EFB≌△DFG,[ASA]BF=GF,BF=CB-CG-GFBF+GF=CB-CG2BF=5-CG,[BF=GF,CB=5]BF=2.5-CG/森唯氏2y=2.5-x/2,[BF=y,CG=x]0