． 已知等差数列{an},公差d≠0,a1,a5,a17成等比数列,则 /=完全正确

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．已知等差数列{an},公差d≠0,a1,a5,a17成等比数列,则/=完全正确．已知等差数列{an},公差d≠0,a1,a5,a17成等比数列,则/=完全正确．已知等差数列{an},公差d≠0,a1

． 已知等差数列{an},公差d≠0,a1,a5,a17成等比数列,则 /=完全正确
． 已知等差数列{an},公差d≠0,a1,a5,a17成等比数列,则 /=
完全正确

． 已知等差数列{an},公差d≠0,a1,a5,a17成等比数列,则 /=完全正确
a1,a5,a17成等比数列
a5^2=a1a17
(a1+4d)^2=a1(a1+16d)
a1^2+8a1d+16d^2=a1^2+16a1d
16d^2=8a1d
a1=2d
所以
/
=/
=/
=/
=26/29

因为a1,a5,a17为等比数列，则有，a5^2=a1*a17,即：(a1+4d)^2=a1*(a1+16d);得：8a1=16d,a1=2d
则/
=（2d+2d+4d+2d+16d)/(2d+d+2d+5d+2d+17d)
=26d/29d
=26/29

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