Check existence of limit with definition

In summary, the conversation discusses using the epsilon-delta definition to check the existence of the limit $\lim_{x\to 0}\frac{x}{x}$ and how to continue the proof. The participants also clarify that since $x\ne 0$, the absolute value of $\frac{x}{x}-1$ is equal to $0$.
  • #1
mathmari
Gold Member
MHB
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Hey! :eek:

I want to check the existence of the limit $\lim_{x\to 0}\frac{x}{x} $ using the definition.

For that do we use the epsilon delta definition?

If yes, I have done the following:

Let $\epsilon>0$. We want to show that there is a $\delta>0$ s.t. if $0<|x-0|<\delta$ then $|f(x)-1|<\epsilon$.

We have that $\left |f(x)-1\right |=\left |\frac{x}{x}-1\right |=\left |\frac{x-1}{x}\right |=\frac{|x-1|}{|x|}$.

How can we continue? (Wondering)
 
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  • #2
Hey mathmari!

Since $0<|x-0|$, it follows that $x\ne 0$.
Therefore $\left|\frac xx -1\right|=0$, isn't it? (Wondering)
 
  • #3
Klaas van Aarsen said:
Since $0<|x-0|$, it follows that $x\ne 0$.
Therefore $\left|\frac xx -1\right|=0$, isn't it? (Wondering)

Ohh yes! Thank you! (Blush)
 

1. What is the definition of a limit?

The limit of a function f(x) as x approaches a point c is the value that f(x) approaches as x gets closer and closer to c. This can be written mathematically as:
limx→c f(x) = L, where L is the limit.

2. How do you check the existence of a limit using the definition?

To check the existence of a limit using the definition, we need to show that for any given value ε (epsilon), there exists a corresponding value δ (delta) such that for all x within a certain distance from c, the difference between f(x) and the limit L is less than ε. If we can find such a δ for any given ε, then the limit exists.

3. What is the importance of checking the existence of a limit using the definition?

Checking the existence of a limit using the definition is important because it provides a rigorous and formal way to prove the existence of a limit. It also allows us to understand the behavior of a function as it approaches a specific point, which is crucial in many areas of mathematics and science.

4. Can a limit exist even if the function is not defined at the point c?

Yes, a limit can exist even if the function is not defined at the point c. This is because the definition of a limit only considers the behavior of the function as it approaches the point c, not necessarily the value of the function at c.

5. Are there any other methods for checking the existence of a limit?

Yes, there are other methods for checking the existence of a limit, such as using the Squeeze Theorem or L'Hopital's Rule. However, the definition of a limit is the most fundamental and reliable method for determining the existence of a limit.

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