已知A、B、C为△ABC的三内角,且其对边分别为a、b、c.若向量
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=
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,
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,向量
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=求A的值;
(2)若
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,三角形面积
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,求b+c的值.
考点分析:
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以下五个命题:
①标准差越小,则反映样本数据的离散程度越大;
②两个随机变量相关性越强,则相关系数越接近1;
③在回归直线方程
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中,当解释变量x每增加1个单位时,则预报变量
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减少0.4个单位;
④对分类变量X与Y来说,它们的随机变量K
2的观测值k越小,“X与Y有关系”的把握程度越大;
⑤在回归分析模型中,残差平方和越小,说明模型的拟合效果越好.
其中正确的命题是:
(填上你认为正确的命题序号).
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已知数列{a
n}满足a
1=1,a
n=log
n(n+1)(n≥2,n∈N
*).定义:使乘积a
1•a
2•…•a
k为正整数的k(k∈N
*)叫做“简易数”.则在[1,2012]内所有“简易数”的和为
.
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a,b∈R,a>b且ab=1,则
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的最小值等于
.
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两圆相交于点A(1,3)、B(m,-1),两圆的圆心均在直线x-y+c=0上,则m+c=
.
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已知
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123936556477359/SYS201310251239365564773010_ST/0.png)
是平面内的单位向量,若向量
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满足
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•(
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-
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)=0,则|
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|的取值范围是
.
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