已知数列
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103101852852183727/SYS201311031018528521837012_ST/0.png)
,则其前n项和S
n=
.
考点分析:
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若(a+b+c)(b+c-a)=3bc,且sinA=2sinBcosC,那么△ABC是
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已知sinα=
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,则cos(π-2α)=
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若不等式x
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的解集为( )
A.(-∞,-3)∪(1,+∞)
B.(-3,1)
C.∅
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△ABC的三边分别为a,b,c,且a=1,B=45°,S
△ABC=2,则△ABC的外接圆的直径为( )
A.5
B.
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D.
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在△ABC中,内角A,B,C的对边分别是a,b,c,若a
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sinB,则A=( )
A.30°
B.60°
C.120°
D.150°
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