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已知数列{An}是一个公差不为0等差数列,且A2=2,并且A3,A6,A12成等比数列,则1A1

已知数列{an}是一个公差不为0等差数列,且a2=2,并且a3,a6∵数列{an}是一个公差不为0等差数列,且a2=2,并且a3,a6,a12成等比数列,∴a62=a3?a12,∴(2+4d)2=(2+d)(2+10d

已知数列{an}是一个公差不为零的等差数列且a2=2 a3 a6a3 a6 a12成等比数列 a6*a6=a3*a12=(a6-3d)(a6+6d)d=1 a2=2 a1=1 an=n 1/(a1*a3)+1/(a2*a4)+1/(a3*a5

已知等差数列an的公差不为零,若a2,a3,a6成等比数列,则a2=a1+da3=a1+2da6=a1+5da3^2=a2*a6(a1+2d)^2=(a1+d)(a1+5d)4a1d+4d^2=6

已知数列an是公差不为零的等差数列a1=1且a1a2a6成等比a1a2a6成等比数列a2 ^2 =a1a6(a1+d)^2=a1(a1+5d)a1^2+2a1d+d^2=a1^2+5a1d3a1d

设数列{an}是公差不为0的等差数列,Sn为前n项和,满足a3解答:解:(1)设数列{an}首项为a1,公差为d,则a3+a12=a1+2d+a 1+11d=2a1+13d,

设数列{an}是公差不为0的等差数列,Sn为前n项和,满足a3,2aa12 成等差数列,∴a3+a12=2×2a5,∴2a1+13d=2(2a1+8d),整理,得2a1+3d=0,(4分)∵S10=60,∴S10=10a1+10×

的首项a1=1,公差d≠0,其中a3,a6,a12成等比数列(1(1)由a3,a6,a12成等比数列及a1=1得,a62=a3 a12,即(1+5d)2=(1+2d) (1+11d),∴d2=3d,∵d≠0,∴d=1,∴an=1+(n

设数列{an}是公差不为0的等差数列,Sn为前n项和,满足a3解答:解:(1)设等差数列{an}的公差为d≠0,∵满足a3,2a5,a12成等差数列,∴4a5=a3+a12,

在公差d≠0的等差数列{an}中,已知a1=-1,且a2,a4,a12(1)由a2,a4,a12三项成等比数列,得a42=a2a12,即(-1+3d)2=(-1+d)(-1+11d),整理得

数列an是公差不为0等差数列,a2=2,a3、a6、a12等比,则1(5/2)T=(5/2){1/(a1a3)+1/(a2a4)+……+1/[ana(n+2)]}=[1/(-1)-1/9]+[1/4-1/14]+[1/9-1/19]+[1/14-1/24

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