3(a1+a3)/2+5(a1+a5)/2=50
3(2a1+2d)/2+5(2a1+4d)/2=50
8a1+13d=50
a1a13=a4a4
a1(a1+12d)=(a1+3d)^2
12a1d=9d^2
a1=3/2d
25d=50
d=2
a1=3
an=3+2(n-1)=2n+1
已知等差数列{an}前n项和为Sn,公差d≠0,且S3+S5=50,a1,a4,a13,成等比数列,求{an}通项公式.需步
已知等差数列{an}前n项和为Sn,公差d≠0,且S3+S5=50,a1,a4,a13,成等比数列,求{an}通项公式.需步
数学人气:806 ℃时间:2019-10-10 03:48:01
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