Proving limits with epsilon and delta

In summary, to prove that as x approaches 0, sin(1/x) has no limit, we start by assuming that the limit exists and then using the definition of a limit to show a contradiction. By choosing epsilon to be 1/2, we can show that there exists a delta such that for all x values within that delta, the difference between sin(1/x) and the assumed limit is less than 1/2. However, by continuing this process, we can find a value of x that leads to a contradiction, proving that the limit does not exist.
  • #1
LBloom
172
0

Homework Statement



Prove that as x approaches 0, sin(1/x) has no limit.

Homework Equations



|x-a|<d and f(x)-L<e

The Attempt at a Solution



my teacher explained it, but i didnt quite get where the contradiction is at the end. We chose epsilon to be 1/2
 
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  • #2
Following your teacher's hint, assume that
[tex]\lim_{x\to 0} \sin(1/x) = L.[/tex]
Then for every ε>0, there exists a η>0 such that 0<|x-0|<η implies |sin(1/x)-L|<ε. Now, let ε=1/2. Then there exists a δ>0 such that 0<|x|<δ implies |sin(1/x)-L|<1/2.

Now that I've started it, can you keep it going until you get a contradiction?
 

Related to Proving limits with epsilon and delta

1. What is the concept of epsilon and delta in proving limits?

Epsilon and delta are mathematical variables used in the formal definition of a limit in calculus. Epsilon represents a small positive number and delta represents a small positive distance. Together, they help us establish a relationship between the input value x and the output value f(x) as x gets closer and closer to a specific value.

2. How do epsilon and delta help prove a limit?

Epsilon and delta help us prove a limit by providing a precise way to determine how close the input value x must be to the limit point in order for the output value f(x) to be within a certain range of the limit. This range is represented by epsilon, and delta helps us find a corresponding range of input values that will result in the desired output range.

3. Can epsilon and delta be used to prove all types of limits?

Yes, epsilon and delta can be used to prove all types of limits, including one-sided limits, infinite limits, and limits at infinity. The concept remains the same, but the calculations may vary slightly depending on the type of limit being considered.

4. How do you know if a limit has been proven using epsilon and delta?

A limit has been proven using epsilon and delta if it can be shown that for any given epsilon, there exists a corresponding delta such that all input values within delta of the limit point will result in output values within epsilon of the limit. This is known as the epsilon-delta definition of a limit.

5. Are there any limitations to using epsilon and delta to prove limits?

While epsilon and delta are powerful tools for proving limits in calculus, they may not always be the most practical or efficient method. In some cases, other techniques such as the squeeze theorem or L'Hopital's rule may be more effective. Additionally, the calculations involved in using epsilon and delta can be complex and time-consuming, so it is important to also consider alternative methods for proving limits.

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