# Limit of an absolute sequence

1. Apr 8, 2008

### ohreally1234

1. The problem statement, all variables and given/known data
Consider the sequence a_n = abs(sin(x))^(1/x)
Find the lim a_n if it exists

2. Relevant equations

None. This is for my calc 2 class.

3. The attempt at a solution

We are studying the sandwich theorem, so I thought 0 < M^(1/x) < abs(sin(x))^(1/x) < 1^(1/x).
(Because I assumed that sequences imply x = 1, 2, 3, 4 ..., so sin(x) never equals 0).

Since M^(1/x) and 1 both tend to 1, I reasoned a_n must go to 1.

Last edited: Apr 8, 2008
2. Apr 8, 2008

### jhicks

Do you mean $$a_{n}=|sin(n)|^{\frac{1}{n}}$$? Second, $$\sqrt[x]{1}$$ does not tend to 0 as x becomes large, nor does even $$\sqrt[x]{\frac{1}{2}}$$. That doesn't make using 1 any less valid, you just made an incorrect assumption.

Last edited: Apr 8, 2008
3. Apr 8, 2008

### ohreally1234

sorry i meant that lim goes to 1. (fixed the typo in original post)

4. Apr 8, 2008

### jhicks

You're almost there, but I'm not convinced. Can you prove the existence of an M and that $$\sqrt[x]{M}$$ goes to 1 as x becomes large? I'm not sure how much rigor is required in your class.

Last edited: Apr 8, 2008
5. Apr 8, 2008

### ohreally1234

I reasoned that M exists because the real numbers are dense.
and you can prove M^(1/x) goes to 1 using the definition of the limit.
Are there any holes in my argument?

6. Apr 8, 2008

Well, it won't equal *exactly* 0, but doesn't the density of the reals imply that it gets arbitrarily close? What is $\liminf_{n\to\infty}\left|\sin(n)\right|$?

7. Apr 8, 2008

### ohreally1234

hmm yeah i thought that part of my argument was a bit shady.
can anyone offer some insights?

8. Apr 9, 2008

### HallsofIvy

Staff Emeritus
The real numbers are dense in what?