直角三角形DEF和直角三角形CEB相似,所以有DE:DF=CE:CB,即DE*CB=DF*EC,
还有DE+EC=DC,即DE=DC-EC,
还有DF*DE/2+5=EC*BC/2,即DF*DE+10=EC*BC,即DF*DE=EC*BC-10,
情况1：当AB=DC=8,AD=BC=6时,6DE=DF*EC,DE=8-EC,DF*DE=6EC-10,
从而,DF*EC=6(8-EC)=48-6EC,6EC=DF*DE+10
即：DF*EC=48-(DF*DE+10)
DF*EC+DF*DE=38
DF(EC+DE)=38
DF=38/8=19/4
情况2：当AB=DC=6,AD=BC=8时,8DE=DF*EC,DE=6-EC,DF*DE=8EC-10,
从而,DF*EC=8(6-EC)=48-8EC,8EC=DF*DE+10,
即：DF*EC=48-(DF*DE+10)
DF*EC+DF*DE=38
DF(EC+DE)=38
DF=38/6=19/3