Suppose and are sequences with positive terms, and the series is known to be convergent. Which of the following statements is true?
A
If , then diverges.
B
If , then converges.
C
If , then diverges.
D
If , then converges.
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검증된 단계별 안내
1
Step 1: Begin by understanding the comparison test and limit comparison test for series. These tests are used to determine the convergence or divergence of a series by comparing it to another series whose behavior is already known.
Step 2: Recall that if \( \sum b_n \) is a convergent series with positive terms, and \( \lim_{n \to \infty} \frac{a_n}{b_n} \) exists and is finite, then the behavior of \( \sum a_n \) (convergence or divergence) will match that of \( \sum b_n \).
Step 3: Analyze the given statements: If \( \lim_{n \to \infty} \frac{a_n}{b_n} = 0 \), this implies that \( a_n \) becomes much smaller than \( b_n \) as \( n \to \infty \). Since \( \sum b_n \) converges, \( \sum a_n \) will also converge.
Step 4: Consider the second statement: If \( \lim_{n \to \infty} \frac{a_n}{b_n} = 1 \), this implies that \( a_n \) and \( b_n \) are asymptotically similar. Since \( \sum b_n \) converges, \( \sum a_n \) will also converge.
Step 5: Evaluate the third statement: If \( \lim_{n \to \infty} \frac{a_n}{b_n} = \infty \), this implies that \( a_n \) grows much faster than \( b_n \). In this case, \( \sum a_n \) will diverge because the terms \( a_n \) do not decrease sufficiently to satisfy the convergence criteria.