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ρ = lim<n→∞>a<n+1>/a<n> = lim<n→∞>(n+2)/(n+1) = 1
收敛半径 R = 1/ρ = 1,
x = -1 时,交错级数收敛; x = 1时,调和级数发散。收敛域 [-1, 1).
x ≠ 0 时,
S(x) = ∑<n=0, ∞>x^n/(n+1) = (1/x)∑<n=0, ∞>x^(n+1)/(n+1)
记 S1(x) =∑<n=0, ∞>x^(n+1)/(n+1),
则 S1'(x) =∑<n=0, ∞>x^n = x/(1-x)
S1(x) = ∫<0, x>S1'(t)dt + S1(0) = ∫<0, x>tdt/(1-t) = -[x+ln(1-x)]
S(x) = -[1+(1/x)ln(1-x)]
于是, 和函数是如下分段函数:
S(x) = -[1+(1/x)ln(1-x)], x ≠ 0;
S(x) = 0, x = 0.
收敛半径 R = 1/ρ = 1,
x = -1 时,交错级数收敛; x = 1时,调和级数发散。收敛域 [-1, 1).
x ≠ 0 时,
S(x) = ∑<n=0, ∞>x^n/(n+1) = (1/x)∑<n=0, ∞>x^(n+1)/(n+1)
记 S1(x) =∑<n=0, ∞>x^(n+1)/(n+1),
则 S1'(x) =∑<n=0, ∞>x^n = x/(1-x)
S1(x) = ∫<0, x>S1'(t)dt + S1(0) = ∫<0, x>tdt/(1-t) = -[x+ln(1-x)]
S(x) = -[1+(1/x)ln(1-x)]
于是, 和函数是如下分段函数:
S(x) = -[1+(1/x)ln(1-x)], x ≠ 0;
S(x) = 0, x = 0.
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