【答案】
分析:由題意易知:
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023213412400337171/SYS201310232134124003371010_DA/0.png)
=1因?yàn)?img src="http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023213412400337171/SYS201310232134124003371010_DA/1.png">=1,先計(jì)算
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023213412400337171/SYS201310232134124003371010_DA/2.png)
的平方的范圍,在開(kāi)方即可.
解答:解:
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023213412400337171/SYS201310232134124003371010_DA/3.png)
=1因?yàn)?img src="http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023213412400337171/SYS201310232134124003371010_DA/4.png">=1,所以
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023213412400337171/SYS201310232134124003371010_DA/5.png)
=2+2sinθ
因?yàn)?≤θ≤π,所以0≤sinθ≤1,所以2+2sinθ≤4,
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023213412400337171/SYS201310232134124003371010_DA/6.png)
≤2
故答案為:2
點(diǎn)評(píng):本題考查向量的模的運(yùn)算、三角函數(shù)在特定區(qū)間上的值域,屬基本運(yùn)算的考查.