0,-3/5,4/5,-15/17,12/13.规律是啥呀?找出规律并写出第9个数,

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0,-3/5,4/5,-15/17,12/13.规律是啥呀?找出规律并写出第9个数,

0,-3/5,4/5,-15/17,12/13.规律是啥呀?找出规律并写出第9个数,
0,-3/5,4/5,-15/17,12/13.规律是啥呀?
找出规律并写出第9个数,

0,-3/5,4/5,-15/17,12/13.规律是啥呀?找出规律并写出第9个数,
0,-3/5,4/5,-15/17,12/13,.
可化为(1-2/2),-(1-2/5),(1-2/10),-(1-15/17),(1-2/26)
通项为X(n)=[(-1)^(n+1)]*[1-2/a(n)]
a(n)-a(n-1)=2n-1
.
a(2)-a(1)=3
a(1)=2
迭代,得a(n)=(3+2n-1)(n-1)/2+2=n^2-1+2=n^2+1
可得通项公式为X(n)=[(-1)^(n+1)]*[1-2/(n^2+1)]
n=9时
得X(9)=40/41