![魔方格](http://img.shitiku.com.cn/uploads/allimg/20191119/20191119004713-65310.png) 如图1, AD⊥l于D,BC⊥l于C,且AD=4,BC=8,E是AB的中点,EF⊥l于F,求EF. ∵AD⊥l于D,BC⊥l,EF⊥l于F, ∴AD∥EF∥BC, ∴ABCD是直角梯形, ∵AE=BE, ∴DF=CF, ∴EF=(AD+BC)÷2=(4+8)÷2=6.
![魔方格](http://img.shitiku.com.cn/uploads/allimg/20191119/20191119004713-88559.png)
如图2, AD⊥l于D,BC⊥l于C,且AD=4,BC=8,E是AB的中点,EF⊥l于F,求EF. ∵AD⊥l于D,BC⊥l,EF⊥l于F, ∴AD∥EF∥BC, ∴△EOF∽△AOD∽△BOC, ∵AD=4,BC=8,E是AB的中点, ∴AD:BC=1:2,EF:AD=1:2, ∴EF=2. 故选D. |