We are asked to find the value of the infinite sum $\sum_{k=1}^{\infty} \frac{1000k^2}{1+k^2}$.

AnalysisInfinite SeriesDivergence TestLimits
2025/3/9

1. Problem Description

We are asked to find the value of the infinite sum k=11000k21+k2\sum_{k=1}^{\infty} \frac{1000k^2}{1+k^2}.

2. Solution Steps

First, we rewrite the expression inside the summation:
1000k21+k2=1000(1+k21)1+k2=1000(1+k2)1+k210001+k2=100010001+k2\frac{1000k^2}{1+k^2} = \frac{1000(1+k^2-1)}{1+k^2} = \frac{1000(1+k^2)}{1+k^2} - \frac{1000}{1+k^2} = 1000 - \frac{1000}{1+k^2}.
Therefore, we have
k=11000k21+k2=k=1(100010001+k2)=k=11000k=110001+k2\sum_{k=1}^{\infty} \frac{1000k^2}{1+k^2} = \sum_{k=1}^{\infty} (1000 - \frac{1000}{1+k^2}) = \sum_{k=1}^{\infty} 1000 - \sum_{k=1}^{\infty} \frac{1000}{1+k^2}.
Since k=11000\sum_{k=1}^{\infty} 1000 diverges to infinity, we need to check if 1000k21+k2\frac{1000k^2}{1+k^2} converges to 00 as kk \to \infty.
We have limk1000k21+k2=limk10001/k2+1=10000\lim_{k \to \infty} \frac{1000k^2}{1+k^2} = \lim_{k \to \infty} \frac{1000}{1/k^2+1} = 1000 \neq 0.
Therefore, by the divergence test, the series diverges.

3. Final Answer

\infty

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