设{an]是一个公差为d(d≠0)的等差数列,它的前10项和s10=110且a1,a2,a4成等比数列,求
证明a1=d
求公差d的值和数列{an}的通项公式
人气：119 ℃ 时间：2019-08-30 14:18:57
解答
A2=A1+d A4=A1+3d
(A2)^2=A1×A4
(A1+d)^2=A1(A1+3d)
(A1)^2+2A1d+d^2=(A1)^2+3A1d
A1d=d^2
d≠0
A1=d
S10=10A1+(1/2)×10×9×d=10A1+45d=55A1=110
A1=2
An=A1+(n-1)d=2n
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