已知四棱锥P-ABCD的底面为直角梯形,AB∥DC,∠DAB=90°,PA⊥底面ABCD,且PA=AD=DC=
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AB=1.
(I)证明:面PAD⊥面PCD;
(II)求AC与PB所成角的余弦值.
考点分析:
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已知函数
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的最小正周期为4π.
(1)求f(x)的单调递增区间;
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设a,b,c,x,y,z是正数,且a
2+b
2+c
2=10,x
2+y
2+z
2=40,ax+by+cz=20,则
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=
.
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由一个数列中部分项按原来次序排列的数列叫做这个数列的子数列,试在无穷等比数列
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,
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,
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101729077540301/SYS201311031017290775403013_ST/2.png)
,…中找出一个无穷等比的子数列,使它所有项的和为
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,则此子数列的通项公式为
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三视图如下的几何体的体积为
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点M(a,b)在由不等式组
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确定的平面区域内,则点N(a+b,a-b)所在平面区域的面积是
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