幂级数求和问题,求指教:∑(n从1到正无穷)(n^2+1)/n * x^2n
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幂级数求和问题,求指教:∑(n从1到正无穷)(n^2+1)/n * x^2n
∑(n从1到正无穷)[(n²+1)/n ] x^(2n)
=∑(n从1到正无穷)nx^(2n)+∑(n从1到正无穷)(1/n)x^(2n)
=x/2∑(n从1到正无穷)2nx^(2n-1)+2∑(n从1到正无穷)[x^(2n)]/2n
=x/2∑(n从1到正无穷)[x^(2n)]′+2∑(n从1到正无穷)∫x^(2n-1)dx(积分区间为0到x)
=x/2[∑(n从1到正无穷)x^(2n)]′+2∫[∑(n从1到正无穷)x^(2n-1)]dx
=x/2[x²/(1-x²)]′+2∫[x/(1-x²)]dx
=x²/(1-x²)²-ln|1-x²|
=∑(n从1到正无穷)nx^(2n)+∑(n从1到正无穷)(1/n)x^(2n)
=x/2∑(n从1到正无穷)2nx^(2n-1)+2∑(n从1到正无穷)[x^(2n)]/2n
=x/2∑(n从1到正无穷)[x^(2n)]′+2∑(n从1到正无穷)∫x^(2n-1)dx(积分区间为0到x)
=x/2[∑(n从1到正无穷)x^(2n)]′+2∫[∑(n从1到正无穷)x^(2n-1)]dx
=x/2[x²/(1-x²)]′+2∫[x/(1-x²)]dx
=x²/(1-x²)²-ln|1-x²|
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