初中数学题如果梯形的两条对角线分
解:
设梯形ABCD的上底为AD下底为BC,中位线为GH,中点G在AB上,中点H在DC上,对角线BD交GH于E,AC交GH于F,
依题意有:GE=EF=FH
--------------------
==>连结DF并延长交BC于K
---------------------
==>GE//AD,FH//AD,
==>ΔBGE∽ΔBAD,ΔCFH∽ΔCAD,
-------------------------------
==>GE/AD=BG/BA=1/2,FH/AC=CH/CD=1/2
==>E、F分别是BD、DK的中点
--------------------------
==>∵EH...全部
解:
设梯形ABCD的上底为AD下底为BC,中位线为GH,中点G在AB上,中点H在DC上,对角线BD交GH于E,AC交GH于F,
依题意有:GE=EF=FH
--------------------
==>连结DF并延长交BC于K
---------------------
==>GE//AD,FH//AD,
==>ΔBGE∽ΔBAD,ΔCFH∽ΔCAD,
-------------------------------
==>GE/AD=BG/BA=1/2,FH/AC=CH/CD=1/2
==>E、F分别是BD、DK的中点
--------------------------
==>∵EH//BC==>∴ΔDEH∽ΔDBC==>EH是ΔDBC的中位线
----------------------------------------------------
==>EH/BC=DE/DB=1/2
-------------------
==>设中位线GH长为3,则GE=EF=FH=1
==>AD=2GE=2,BC=2EH=4
==>∴AD/BC=2/4=1/2
-------------------
不明之处请指出~~
。
收起