等差数列{An}中,An不等于0,An-1—An^2—An+1=0,S2n-1=38.则n等于?A10 B19 C20 D38

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$等差数列{An}中,An不等于0,An-1—An^2—An+1=0,S2n-1=38.则n等于?A10 B19 C20 D38$

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等差数列{An}中,An不等于0,An-1—An^2—An+1=0,S2n-1=38.则n等于?A10 B19 C20 D38
等差数列{An}中,An不等于0,An-1—An^2—An+1=0,S2n-1=38.则n等于?
A10 B19 C20 D38

等差数列{An}中,An不等于0,An-1—An^2—An+1=0,S2n-1=38.则n等于?A10 B19 C20 D38
选A
An+1-An^2+An-1=0
2An=An+1 + An-1
所以An^2=2An
因为An不等于0
所以An等于2
S2n-1=(2n-1)*2=38
所以n=10

选择题不会做的话一个个带进去验算。。

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