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单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,一、选择题(每题,4,分,共,16,分),1.,(,2010,临沂高二检测)数列,a,n,的前,n,项和为,S,n,若,a,n,=,则,S,5,等于,( ),(,A,),1,(,B,) (,C,) (,D,),【,解析,】,选,B.,S,5,=,2.(2010,福建高考,),设等差数列的前,n,项和为,S,n,.,若,a,1,=-11,a,4,+a,6,=-6,则当,S,n,取最小值时,,n,等于,( ),(,A,),6,(,B,),7,(,C,),8,(,D,),9,【,解析,】,选,A.,由,a,4,+a,6,=-6,得,a,5,=-3,-11+4d=-3,d=2,S,n,=-11n+ 2=(n-6),2,-36.,当,n=6,时,,S,n,有最小值,-36.,3.,已知数列,a,n,对任意的,p,qN,*,,有,a,p+q,=a,p,+a,q,且,a,2,=-6,则,a,10,=( ),(,A,),-165,(,B,),-33,(,C,),-30,(,D,),-21,【,解析,】,选,C.,由题意知,,a,10,=a,2,+a,8,=a,2,+2a,4,=a,2,+4a,2,=5a,2,=5(-6)=-30.,4.,(,2010,开原高二检测)数列,a,n,的前,n,项和为,S,n,=n,2,-9n,且第,k,项满足,5a,k,8,则,k=( ),(A)9 (B)8 (C)7 (D)6,【,解析,】,选,B.,当,n=1,时,,a,1,=S,1,=-8,当,n2,时,,a,n,=S,n,-S,n-1,=2n-10,综上可知,a,n,=2n-10,令,52k-108,得,k9,又,kN,*,k=8.,二、填空题(每题,4,分,共,8,分),5.,(,2010,哈尔滨高二检测)数列,b,n,的通项公式,b,n,=-2n+49.,则,b,n,的前,n,项和取得最大值时,,n,等于,_.,【,解析,】,由题意知,,d0,S,13,0,S,13,0,即,- d0,S,13,0,又由(,1,)知,,d0,数列前,6,项为正,从第,7,项起为负,.,数列前,6,项和最大,.,8.,数列,a,n,满足,a,1,=1, (nN,*,).,(1),求证:数列, ,是等差数列;,(2),设,T,n,=a,1,a,2,+a,2,a,3,+,+a,n,a,n+1,,若,T,n,a,恒成立,求,a,的取值范围,.,【,解析,】,数列,T,n,是递增数列,,当,n=1,时,,T,n,有最小值,T,1,=,a,a,的取值范围是(,-,.,9.,(,10,分)已知各项均为正数的数列,a,n,中,,a,1,=1,S,n,是数列,a,n,的前,n,项和,对任意,nN,*,有,2S,n,=2pa,n,2,+pa,n,-p(pR).,(,1,)求常数,p,的值;,(,2,)求数列,a,n,的通项公式,.,【,解题提示,】,由含有通项,a,n,的前,n,项和,S,n,的表达式求,a,n,时,一般是先在,S,n,表达式中将,n,换作,n-1,构造,S,n-1,的表,达式,利用,a,n,=,来探求,a,n,.,【,解析,】,
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