等差数列an前n项和为Sn,且满足2S5-13a4+5a8=10,下列数恒为常数的是A.a8 B.S9 C.a17 D.S17

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等差数列an前n项和为Sn,且满足2S5-13a4+5a8=10,下列数恒为常数的是A.a8B.S9C.a17D.S17等差数列an前n项和为Sn,且满足2S5-13a4+5a8=10,下列数恒为常数

等差数列an前n项和为Sn,且满足2S5-13a4+5a8=10,下列数恒为常数的是A.a8 B.S9 C.a17 D.S17
等差数列an前n项和为Sn,且满足2S5-13a4+5a8=10,下列数恒为常数的是
A.a8 B.S9 C.a17 D.S17

等差数列an前n项和为Sn,且满足2S5-13a4+5a8=10,下列数恒为常数的是A.a8 B.S9 C.a17 D.S17
2s5-13a4+5a8=10
2(2a1+4d)*5/2-13(a1+3d)+5(a1+7d)=10
10a1+20d-13a1-39d+5a1+35d+10
2a1+16d=10
1)a1+8d=5
a9=5
2)设Sn为常数,则[2a1+(n-1)d]*n/2=na1+n(n-1)d/2=C(a1+8d) (C为任意常数)
n(n-1)/2=8n 即n=17,或n=0(舍),成立
故S17为常数,S17=85

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