(2003•资阳)如图,在△ABC中,已知∠ACB=90°,CD⊥AB于D,AC=
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232441953884086/SYS201310212324419538840016_ST/0.png)
,BD=3.
(1)请根据下面求cosA的解答过程,在横线上填上适当的结论,使解答正确完整,
∵CD⊥AB,∠ACB=90°∴AC=______cosA,______=AC•cosA
由已知AC=6
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232441953884086/SYS201310212324419538840016_ST/1.png)
,BD=3,∴
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232441953884086/SYS201310212324419538840016_ST/2.png)
=AB cosA=(AD+BD)cosA=(
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232441953884086/SYS201310212324419538840016_ST/3.png)
cosA+3)cosA,设t=cosA,则t>0,且上式可化为
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232441953884086/SYS201310212324419538840016_ST/4.png)
t
2+______
考点分析:
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