已知:如圖1,M是定長(zhǎng)線段AB上一定點(diǎn),C、D兩點(diǎn)分別從M、B出發(fā)以1cm/s、3cm/s的速度沿直線BA向左運(yùn)動(dòng),運(yùn)動(dòng)方向如箭頭所示(C在線段AM上,D在線段BM上)
![](http://hiphotos.baidu.com/zhidao/pic/item/d1a20cf431adcbef7d0f2eb2afaf2edda3cc9f4e.jpg)
(1)若AB=10cm,當(dāng)點(diǎn)C、D運(yùn)動(dòng)了2s,求AC+MD的值.
(2)若點(diǎn)C、D運(yùn)動(dòng)時(shí),總有MD=3AC,直接填空:AM=______AB.
(3)在(2)的條件下,N是直線AB上一點(diǎn),且AN-BN=MN,求
的值.
(1)當(dāng)點(diǎn)C、D運(yùn)動(dòng)了2s時(shí),CM=2cm,BD=6cm
∵AB=10cm,CM=2cm,BD=6cm
∴AC+MD=AB-CM-BD=10-2-6=2cm
(2)
(3)當(dāng)點(diǎn)N在線段AB上時(shí),如圖
![](http://hiphotos.baidu.com/zhidao/pic/item/72f082025aafa40f41611f6ca864034f79f019df.jpg)
∵AN-BN=MN,又∵AN-AM=MN
∴BN=AM=
AB,∴MN=
AB,即
=.
當(dāng)點(diǎn)N在線段AB的延長(zhǎng)線上時(shí),如圖
![](http://hiphotos.baidu.com/zhidao/pic/item/a5c27d1ed21b0ef4f68949efdec451da81cb3e1a.jpg)
∵AN-BN=MN,又∵AN-BN=AB
∴MN=AB,即
=1.綜上所述
=
或1