在△ABC中,∠C=90°,cosB=
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,a=
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,则b=
.
考点分析:
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如图,在平行四边形ABCD中,过B作BE⊥CD,垂足为点E,连接AE,F为AE上一点,且∠BFE=∠C.
(1)求证:△ABF∽△EAD;
(2)若AB=4,∠BAE=30°,求AE的长;
(3)在(1)(2)的条件下,若AD=3,求BF的长.(计算结果可含根号)
查看答案
观察下列分母有理化的运算.
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/0.png)
=
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/1.png)
-1,
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/2.png)
=
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/3.png)
-
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/4.png)
,
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/5.png)
=
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/6.png)
-
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/7.png)
…
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/8.png)
=
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/9.png)
-
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/10.png)
,
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/11.png)
=
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/12.png)
-
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/13.png)
利用上面的规律计算:
(
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/14.png)
+
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/15.png)
+
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/16.png)
+…+
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/17.png)
+
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/18.png)
)(1+
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131103000455182603776/SYS201311030004551826037022_ST/19.png)
)
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如图,在4×3的正方形方格中,△ABC和△DEC的顶点都在边长为1的小正方形的顶点上.
(1)填空:∠ABC=______°,BC=______
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某商场今年2月份的营业额为400万元,3月份的营业额比2月份增加10%,5月份的营业额达到633.6万元.求3月份到5月份营业额的月平均增长率.
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