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1. cho hinh thang ABCD (AB//CD).Goi O la giao diem cua 2 duong cheo,qua O ke duong thang song song voi 2 day cat AD,BC thu tu o E,F. Goi I,Q thu tu la trung diem cua AB,CD.
a, CM:
+
=1
b,OE=OF
c. Ba diem O,I,Q thang hang.
a, CM:
b,OE=OF
c. Ba diem O,I,Q thang hang.