B组因材施教备选练习1设等差数列an的前n项和为Sn,已知(a61)32 013(a61)1,(a2 0081)22 013(a2 0081)1,则下列结论中正确的是()AS2 0132 013,a2 008a6CS2 0132 013,a2 008a6DS2 0132 013,a2 008a6解析:依题意,构造函数f(x)x32 013x,易知函数f(x)x32 013x为奇函数,由f(a61)1,f(a2 0081)1,得a61(a2 0081),a6a2 0082,数列an是等差数列,S2 0132 013,排除C、D;函数f(x)x32 013x为增函数,且f(a2 0081)f(a61),a2 0081a61,即a2 0080,An2.,数列An是首项为A12,公比为的等比数列Sn(42) ()n1(2)由(1)得anlog2Anlog22,tan 1tan(n1)n,tan ntan(n1)1,nN*.Tntan a2tan a4tan a4tan a6tan a2ntan a2n2,Tntan 2tan 3tan 3tan 4tan(n1)tan(n2)n.