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  • - [Instructor] So right over here,

  • we have the graph of y is equal to one over x squared.

  • And my question to you is what is the limit

  • of one over x squared as x approaches zero?

  • Pause this video, and see if you can figure that out.

  • Well, when you try to figure it out,

  • you immediately see something interesting

  • happening at x equals zero.

  • The closer we get to zero from the left,

  • you take one over x squared,

  • it just gets larger and larger and larger.

  • It doesn't approach some finite value.

  • It's unbounded, has no bound.

  • And the same thing is happening

  • as we approach from the right.

  • As we get values closer and closer to zero from the right,

  • we get larger and larger values

  • for one over x squared without bound.

  • So terminology that folks will sometimes use,

  • where they're both going in the same direction,

  • but it's unbounded, is they'll say this limit is unbounded.

  • In some context, you might hear teachers say

  • that this limit does not exist or,

  • and it definitely does not exist if you're thinking about

  • approaching a finite value.

  • In future videos, we'll start to introduce ideas of infinity

  • and notations around limits and infinity,

  • where we can get a little bit more specific

  • about what type of limit this is.

  • But with that out of the way,

  • let's look at another scenario.

  • This right over here, you might recognize

  • as the graph of y is equal to one over x.

  • So I'm going to ask you the same question.

  • Pause this video, and think about

  • what's the limit of one over x as x approaches zero?

  • Pause this video, and figure it out.

  • All right, so here, when we approach from the left,

  • we get more and more and more negative values.

  • While we, when we approach from the right,

  • we're getting more and more positive values.

  • So in this situation,

  • where we're not getting unbounded in the same direction,

  • the previous example, we were both,

  • we were being unbounded in the positive direction.

  • But here, on the, from the left,

  • we're getting unbounded in the negative direction.

  • While from the right, we're getting unbounded

  • in the positive direction.

  • And so when you're thinking about the limit

  • as you approach a point, if it's not even approaching

  • the same value or even the same direction,

  • you would just clearly say that this limit does not exist,

  • does

  • not

  • exist.

  • So this is a situation, where you would not even say

  • that this is an unbounded limit

  • or that the limit is unbounded.

  • Because you're going in two different directions when you

  • approach from the right and when you approach from the left,

  • you would just clearly say does not exist.

- [Instructor] So right over here,

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A2 初級 美國腔

無限極限 |限制和連續性 | AP微積分AB |可汗學院(Unbounded limits | Limits and continuity | AP Calculus AB | Khan Academy)

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    yukang920108 發佈於 2022 年 06 月 30 日
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