作DH垂直于AC交AC于点H设△ABC的面积为S,平行四边形DFCE的面积为S'则 根号S1:根号S=AD:AB.(1)根号S2:根号S=BD:AB.(2)(1)/(2)得AD:BD=根号S1:根号S2因为DH×BF=2×S2所以DH=2×S2/BFS'=DH×CF=2×S2×(CF/BF)=2×...