题目内容
(2005•滨州)在Rt△ABC中,若∠C=90°,AC=1,BC=2,则下列结论中正确的是( )A.sinB=
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/201310201206358615300806/SYS201310201206358615300002_ST/0.png)
B.cosB=
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/201310201206358615300806/SYS201310201206358615300002_ST/1.png)
C.tanB=2
D.cotB=
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/201310201206358615300806/SYS201310201206358615300002_ST/2.png)
【答案】分析:先根据勾股定理求出AB,再根据锐角三角函数的定义解答.
解答:解:∵在Rt△ABC中,∠C=90°,AC=1,BC=2,
∴AB=
,sinB=
,cosB=
,tanB=
,cotB=2.
故选A.
点评:本题考查锐角三角函数的定义即:在直角三角形中,锐角的正弦为对边比斜边,余弦为邻边比斜边,正切为对边比邻边.
解答:解:∵在Rt△ABC中,∠C=90°,AC=1,BC=2,
∴AB=
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/201310201206358615300806/SYS201310201206358615300002_DA/0.png)
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/201310201206358615300806/SYS201310201206358615300002_DA/1.png)
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/201310201206358615300806/SYS201310201206358615300002_DA/2.png)
![](http://thumb.1010pic.com/pic6/res/czsx/web/STSource/201310201206358615300806/SYS201310201206358615300002_DA/3.png)
故选A.
点评:本题考查锐角三角函数的定义即:在直角三角形中,锐角的正弦为对边比斜边,余弦为邻边比斜边,正切为对边比邻边.
![](http://thumb2018.1010pic.com/images/loading.gif)
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