幂级数展开式,求高人解救加鄙视、、、感激不尽

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幂级数展开式,求高人解救加鄙视、、、感激不尽幂级数展开式,求高人解救加鄙视、、、感激不尽幂级数展开式,求高人解救加鄙视、、、感激不尽(arctan(x))''=1/(1+x²)=∑{0≤n}(

幂级数展开式,求高人解救加鄙视、、、感激不尽
幂级数展开式,求高人解救加鄙视、、、
感激不尽

幂级数展开式,求高人解救加鄙视、、、感激不尽
(arctan(x))' = 1/(1+x²) = ∑{0 ≤ n} (-1)^n·x^(2n).
积分得arctan(x) = ∑{0 ≤ n} (-1)^n·x^(2n+1)/(2n+1).
于是arctan(x)/x = ∑{0 ≤ n} (-1)^n·x^(2n)/(2n+1).
故(1+x²)·arctan(x)/x = ∑{0 ≤ n} (-1)^n·x^(2n)/(2n+1)+∑{0 ≤ n} (-1)^n·x^(2n+2)/(2n+1)
= 1+∑{1 ≤ n} (-1)^n·x^(2n)/(2n+1)+∑{0 ≤ n} (-1)^n·x^(2n+2)/(2n+1)
= 1+∑{1 ≤ n} (-1)^n·x^(2n)/(2n+1)+∑{1 ≤ n} (-1)^(n-1)·x^(2n)/(2n-1)
= 1+∑{1 ≤ n} (-1)^(n-1)·(1/(2n-1)-1/(2n+1))·x^(2n)
= 1+∑{1 ≤ n} (-1)^(n-1)·2·x^(2n)/(4n²-1).