Sequence satisfying a condition for all n

In summary, the conversation discusses a sequence of positive numbers that satisfies a certain condition, and the goal is to show that the sequence approaches infinity. The approach involves making the sequence into a geometric sequence and taking the logarithm. The attempt at a solution involves comparing different terms of the sequence and considering the limit of the ratio of consecutive terms.
  • #1
StarTiger
9
1

Homework Statement



Suppose that a sequence {s_n} of positive numbers satisfies the condition s_(n+1) > αs_n for all n where α > 1. Show that s_n → ∞

My teacher mentioned something about making it into a geometric sequence and taking the log. I'm just confused.

Homework Equations





The Attempt at a Solution

 
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  • #2
You can start with s2 > as1. Now what about s3? Can you compare it to s2 and s1? Continue...
 
  • #3
StarTiger said:

Homework Statement



Suppose that a sequence {s_n} of positive numbers satisfies the condition s_(n+1) > αs_n for all n where α > 1. Show that s_n → ∞

My teacher mentioned something about making it into a geometric sequence and taking the log. I'm just confused.

Homework Equations





The Attempt at a Solution

So [itex]s_2> a s_n[/itex], [itex]s_3> a s_2> a(a s_1)= a^2 s_1[/itex], [itex]s_4> a s_3> a(a^2 s_1)= a^3 s_1[/itex]. So [itex]s_n> [/itex] a to what power times [itex]s_1[/itex]? What does that have to do with a "geometric sequence"?
 
  • #4
If [tex](s_n)[/tex] is a sequence and the limit [tex]\lim_{n \to \infty}|s_{n+1} / {s_n}| = L [/tex] exists and [tex]L < 1[/tex], then [tex]\lim s_n[/tex] converges. If not, what do you think happens?
 

1. What does it mean for a sequence to satisfy a condition for all n?

When a sequence satisfies a condition for all n, it means that the condition is true for every term in the sequence, no matter how large or small n (the term number) is.

2. Can you give an example of a sequence that satisfies a condition for all n?

One example is the sequence 2^n, where n is a term number. This sequence satisfies the condition that each term is equal to 2 raised to the power of the term number, for all n.

3. How can you prove that a sequence satisfies a condition for all n?

To prove that a sequence satisfies a condition for all n, you can use mathematical induction. This involves showing that the condition holds for the first term in the sequence, and then assuming it holds for some arbitrary term k, and using that assumption to show that the condition also holds for the next term k+1. This process can be repeated indefinitely, proving that the condition holds for all terms in the sequence.

4. What is the importance of sequences satisfying a condition for all n in mathematics?

Sequences satisfying a condition for all n are important in mathematics because they allow us to make generalizations and prove properties about the sequence as a whole. By knowing that a condition holds for all terms in the sequence, we can confidently make statements about the behavior and properties of the sequence, which can then be applied to solve problems and make predictions in various fields of mathematics.

5. Can a sequence satisfy multiple conditions for all n?

Yes, a sequence can satisfy multiple conditions for all n. For example, the sequence n^2 satisfies the conditions that each term is a perfect square and that each term is greater than the previous term, for all n. In general, a sequence can satisfy any number of conditions as long as they hold for all terms in the sequence.

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