1.6.365 AP Calculus Exam Limits

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Discussion Overview

The discussion revolves around the evaluation of limits in the context of an AP Calculus exam question, specifically focusing on whether certain limits exist based on the behavior of a function at specific points. Participants analyze various statements regarding limits and continuity.

Discussion Character

  • Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant claims that a limit does not exist if the function values differ when approaching from the left and right, indicating a misunderstanding of the notation used.
  • Another participant clarifies that the terms "from the left and from the right" correspond to the notation "$\pm$" and asserts that statement c) is false based on the differing one-sided limits at x=4.
  • Several limits are evaluated:
    • a) The limit as x approaches 2 exists and is equal to 2, but the function is not continuous at that point.
    • b) The limit as x approaches 3 exists and is equal to 5, with continuity at that point.
    • c) The limit as x approaches 4 does not exist due to differing left-hand and right-hand limits.
    • d) The limit as x approaches 5 exists and is equal to 6, with continuity at that point.
    • e) The function is continuous at x=3, as the limit and function value are equal.
  • One participant notes a visual cue regarding a "disconnected gap" in the function, suggesting it aids in understanding the limits involved.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of limits and continuity, particularly regarding the existence of the limit at x=4. There is no consensus on the understanding of the notation and its implications for the limits discussed.

Contextual Notes

Some assumptions about the function's behavior and the definitions of limits may not be fully articulated, leading to potential misunderstandings in the discussion.

karush
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ok I chose c being false, since a limit does not exist if f(x) is different coming from $\pm$
 
Last edited:
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You need to look at left-hand and right-hand limits. I don't see where "$\pm$" comes into it.
 
I believe that "from the left and from the right" was what Karush meant by "\pm!

Yes, Karush, "c" is the only one that is false.

a) \lim_{x\to 2} f(x) exists.
True. The limit is 2. (f(2)= 1 so f is NOT continuous there.)

b) \lim_{x\to 3} f(x) exists.
True. The limit is 5. (Further f(3)= 5 so f is continuous there.)

c) \lim_{x\to 4} f(x) exists.
False. The "limit from the left", \lim_{x\to 4^-} f(x), is 2 while the "limit from the right", \lim_{x\to 4^+} f(x), is 4. Since the two one-sided limits are not the same the limit itself does not exist.

d) \lim_{x\to 5} f(x) exists.
True. The limit is 6. (Further f(5)= 6 so f is continuous there.)

e) f is continuous at x= 3.
True. As I said in (b), \lim_{x\to 3} f(x) and f(3) both exist and are equal.
 
ok I think the big visual hint on this one was the obvious disconnected gap.

mahalo everyone the comments really increase the insight on these.
 

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