题目内容
在Rt△ABC中,∠C=90°,若BC=2,cosB=![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131021230629661748073/SYS201310212306296617480005_ST/0.png)
A.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131021230629661748073/SYS201310212306296617480005_ST/1.png)
B.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131021230629661748073/SYS201310212306296617480005_ST/2.png)
C.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131021230629661748073/SYS201310212306296617480005_ST/3.png)
D.
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131021230629661748073/SYS201310212306296617480005_ST/4.png)
【答案】分析:根据题中所给的条件,在直角三角形中解题.根据角的余弦值与三角形边的关系及勾股定理,可求出AB和AC的长.
解答:解:在Rt△ABC中,
cosB=
=
,
∴AB=6,
∴AC=
=4
.
故选C.
点评:本题主要考查解直角三角形时会运用勾股定理解答问题.
解答:解:在Rt△ABC中,
cosB=
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131021230629661748073/SYS201310212306296617480005_DA/0.png)
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131021230629661748073/SYS201310212306296617480005_DA/1.png)
∴AB=6,
∴AC=
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131021230629661748073/SYS201310212306296617480005_DA/2.png)
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/20131021230629661748073/SYS201310212306296617480005_DA/3.png)
故选C.
点评:本题主要考查解直角三角形时会运用勾股定理解答问题.
![](http://thumb2018.1010pic.com/images/loading.gif)
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