如图,形如三角板的△ABC中,∠ACB=90°,∠ABC=45°,BC=12cm,形如矩形量角器的半圆O的直径DE=12cm,矩形DEFG的宽EF=6cm,矩形量角器以2cm/s的速度从左向右运动,在运动过程中,点D、E始终在BC所在的直线上,设运动时间为x(s),矩形量角器和△ABC的重叠部分的面积为S(cm
2).当x=0(s)时,点E与点C重合.(图(3)、图(4)、图(5)供操作用).
(1)当x=3时,如图(2),S=______cm
2,当x=6时,S=______cm
2,当x=9时,S=______cm
2;
(2)当3<x<6时,求S关于x的函数关系式;
(3)当6<x<9时,求S关于x的函数关系式;
(4)当x为何值时,△ABC的斜边所在的直线与半圆O所在的圆相切?
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考点分析:
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如图,已知:△ABC内接于⊙O,点D在OC的延长线上,sinB=
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103102404751844486/SYS201311031024047518444012_ST/0.png)
,∠D=30度.
(1)求证:AD是⊙O的切线;
(2)若AC=6,求AD的长.
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如图所示,AB是⊙O的直径,AD是弦,∠DBC=∠A.
(1)求证:BC与⊙O相切;
(2)若OC∥AD,OC交BD于点E,BD=6,CE=4,求AD的长.
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已知:如图,AB是⊙O的直径,AB=6,延长AB到点C,使BC=AB,D是⊙O上一点,DC=
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103102404751844486/SYS201311031024047518444010_ST/0.png)
.求证:
(1)△CDB∽△CAD;
(2)CD是⊙O的切线.
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如图,点A,B,C,D在⊙O上,AB=AC,AD与BC相交于点E,AE=
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103102404751844486/SYS201311031024047518444009_ST/0.png)
ED,延长DB到点F,使FB=
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BD,连接AF.
(1)证明:△BDE∽△FDA;
(2)试判断直线AF与⊙O的位置关系,并给出证明.
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如图,已知AB为⊙O的直径,直线BC与⊙O相切于点B,过A作AD∥OC交⊙O于点D,连接CD.
(1)求证:CD是⊙O的切线;
(2)若AD=2,直径AB=6,求线段BC的长.
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