Understanding Limits: Explaining Left and Right Limits in Simple Terms

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Discussion Overview

The discussion revolves around the concept of limits in calculus, specifically focusing on left and right limits as they approach a particular value. Participants seek clarification on the definitions and implications of these limits, with an emphasis on understanding them in simpler terms.

Discussion Character

  • Conceptual clarification
  • Homework-related

Main Points Raised

  • One participant asks for a simplified explanation of the limits \displaystyle \lim_{x \to 3^+}\frac{1}{x} and \displaystyle \lim_{x \to 3^-}\frac{1}{x}, expressing difficulty with epsilon-delta definitions.
  • Another participant explains that the plus sign indicates approaching 3 from values greater than 3 (e.g., 3.1, 3.01), while the minus sign indicates approaching from values less than 3.
  • A participant questions the choice of starting point (3.1) for the right limit, leading to a clarification that the focus is on getting close to 3, regardless of the specific starting point.
  • One participant notes that left and right limits can differ, mentioning jump discontinuities and providing the Heaviside Function as an example.
  • A participant suggests a specific limit problem for others to evaluate, highlighting the need to check both left and right limits.

Areas of Agreement / Disagreement

Participants generally agree on the definitions of left and right limits, but there is no consensus on the implications of differing limits, as some participants introduce examples and concepts that may not be universally accepted.

Contextual Notes

Some participants express uncertainty about the epsilon-delta definition of limits, indicating a potential limitation in their understanding of formal definitions. The discussion also touches on the concept of discontinuities without fully resolving the implications of these examples.

Poly1
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Could someone explain what things like \displaystyle \lim_{x \to 3^+}\frac{1}{x} and \displaystyle \lim_{x \to 3^-}\frac{1}{x} are supposed to be?

I googled and it gave me epsilon delta stuff. I'm not smart enough for that. (Doh)

I guess I'm asking if anyone could give a dumbed down explanation of sorts. :D
 
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Poly said:
Could someone explain what things like \displaystyle \lim_{x \to 3^+}\frac{1}{x} and \displaystyle \lim_{x \to 3^-}\frac{1}{x} are supposed to be?

I googled and it gave me epsilon delta stuff. I'm not smart enough for that. (Doh)

I guess I'm asking if anyone could give a dumbed down explanation of sorts. :D

Plus means approaching 3 from the right so 3.1, 3.01, 3.001 etc
I bet you can guess what minus means.
 
Why did you start with 3.1?
 
Poly said:
Why did you start with 3.1?

It isn't really a starting point. I was just emphasizing approaching from the right. We could start at 100 but the goal is to approach 3 and get really close to 3. Really close as in 3.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001
 
Thanks. Did I read that sometimes \lim_{x \to a^{+}}f(x) and \lim_{x \to a^{-}}f(x) can be different? How's that?
 
Poly said:
Thanks. Did I read that sometimes \lim_{x \to a^{+}}f(x) and \lim_{x \to a^{-}}f(x) can be different? How's that?

That is true. You can have jump discontinuities or one side going to neg inf and the other to pos inf.
Look at the Heaviside Function has an example
 
Here is an example you can try:
$$
\lim_{x\to 1}\frac{x^2 - 2x - 3}{x-1}
$$
You need to check the left and right limit.
 

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