如图所示.梯形ABCD中,AD∥BC,BD,AC交于O点,过O的直线分别交AB,CD于E,F,且EF∥BC.AD=12厘米,BC=20厘米.求EF.
问题描述:
如图所示.梯形ABCD中,AD∥BC,BD,AC交于O点,过O的直线分别交AB,CD于E,F,且EF∥BC.AD=12厘米,BC=20厘米.求EF.
答
∵AD∥BC,EF∥BC,
∴
=AD BC
=OA OC
=12 20
,3 5
又
=OE BC
=OA AC
,3 8
=OF AD
=OC AD
,5 8
∴OE=
BC=3 8
,OF=15 2
AD=5 8
,15 2
∴EF=OE+OF=15.