Chapter 2: Problem 4
Prove that if \(s_{n} \rightarrow \infty\) then \(-s_{n} \rightarrow-\infty\).
Short Answer
Expert verified
If \(s_{n} \to \infty\), then \(-s_{n} \to -\infty\) because multiplying by \(-1\) reverses the limit direction.
Step by step solution
01
Understanding the Limit Condition
We begin with the assumption that the sequence \( s_n \) diverges to infinity. This means that for every positive number \( M \), there exists a positive integer \( N \) such that for all integers \( n > N \), the inequality \( s_n > M \) holds.
02
Transforming the Sequence
To find the behavior of the sequence \( -s_n \), we multiply the sequence \( s_n \) by \(-1\). Since multiplying by \(-1\) reverses inequalities, if \( s_n > M \), then \(-s_n < -M\).
03
Evaluating the New Sequence
Given that \( -s_n < -M \) for all integers \( n > N \), this inequality indicates that the sequence \( -s_n \) is becoming increasingly large negative values as \( n \) increases.
04
Conclude the Limit Behavior
The inequality \( -s_n < -M \) for all \( n > N \) shows that for any positive number \( M \), there exists a corresponding \( N \) such that for all \( n > N \), \( -s_{n} \) is less than \(-M\). This proves that \( -s_n \rightarrow -infty \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Divergence
Divergence in sequences often refers to a sequence not settling at a particular value. Instead, it continues growing larger or smaller without bound. In this context, we're discussing the scenario where a sequence diverges to infinity. This implies that as you keep progressing through the sequence (by going to larger values of index \( n \)), the sequence values continue increasing. They grow without constraint to infinity, meaning they surpass any finite number, no matter how large.
- Consider a sequence \( s_n \) that diverges to infinity. For any given large number \( M \), there exists an index \( N \). Beyond this index, all sequence values \( s_n \) are greater than \( M \).
- This formalizes the idea that the sequence 'runs away' to infinity beyond a certain point, which we could identify with the index \( N \).
Inequalities
Inequalities are mathematical expressions involving less than (<), more than (>), less than or equal to (≤), or more than or equal to (≥) signs. They are crucial when discussing limits, especially when sequences diverge.
- For the sequence \( s_n \), the condition \( s_n > M \) for all sufficiently large \( n \) signifies divergence to infinity.
- When you negate the sequence, you flip the inequality sign. If \( s_n > M \), then after negating, you get \(-s_n < -M\).
- This flipping is important as it directly reflects on how the sequence is being transformed, which, in this example, leads \(-s_n\) to approach negative infinity.
Sequence Transformation
Sequence transformations involve altering a sequence in a mathematical operation to study a different property or behavior. In our exercise, the transformation involved multiplying the sequence by \(-1\).
- This particular transformation is straightforward: every term in the sequence is negated.
- Negation changes not only the terms but also how these terms relate to infinity, pivotal in determining if and how the limit of the sequence is altered.
- As shown, the condition \( s_n > M \) transforms to \(-s_n < -M\), illustrating the principle of sequence transformation and its implications on limit behavior.