详细过程如下:已知:DF:CD=X ∴DF=X*CDS△CEF=CF*ED*0.5=【CD-DF】*【0.5*AD】*0.5=【(1-X)*CD】*AD*0.25 =0.25*(1-X)*【AD*CD】 =0.25*(1-X)*【S正ABCD】答案:0.25*(1-X)希望帮到你喽!