在梯形ABCD中,AD//BC,對角線ACBD,且AC=12,BD=9,則此梯形的
中位線長是( ).
A.B.C.D.
C

試題分析:過點D作,交BC于點E,
所以可得DE=AC,AD=CE,又因為,所以BD⊥DE,根據(jù)勾股定理,,而梯形的中位線等于上底與下底的和的一半,所以梯形的中位線長為
點評:解決本小題的關(guān)鍵是作輔助線,進而就可以利用數(shù)量關(guān)系和勾股定理進行求解.
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