Why Did My Math Answer Get Marked Incorrect?

  • Context: High School 
  • Thread starter Thread starter UrbanXrisis
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Discussion Overview

The discussion revolves around a math question that a participant had marked incorrect. The focus is on understanding the interpretation of a graph and the notation used, particularly regarding the ceiling function and its representation in the graph.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether the notation should be interpreted as ceiling(0.5x), suggesting ambiguity in the scanned image.
  • Another participant agrees with the initial graph but suggests consulting the person who graded the question for clarity.
  • A claim is made that the required answer is a straight line segment from (-1,-2) to (1,2).
  • There is a discussion about the meaning of the brackets, with one participant asserting that they imply the greatest integer function.
  • A participant acknowledges a misunderstanding regarding the brackets and suggests that the solution may be correct if the brackets indicate ceiling.
  • Another participant points out an error in the interpretation of the graph, stating that the ceiling of 1 is 1, not 2, and corrects their earlier plotting mistake.
  • A later post raises a question about the use of "open circles" in the graph, discussing their implications for interval inclusion.

Areas of Agreement / Disagreement

Participants express differing interpretations of the notation and the graph, with no consensus reached on the correct understanding of the problem or the grading criteria.

Contextual Notes

There are limitations in the clarity of the scanned image and the notation used, which may affect participants' interpretations. The discussion also highlights unresolved assumptions about the meaning of the brackets and the representation of intervals in the graph.

UrbanXrisis
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Why did I get this Math Question Wrong?

http://home.earthlink.net/~urban-xrisis/IMG_0373.jpg
 
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Is it supposed to be [0.5x], meaning ceiling? It's hard to make out on my screen
 
i get the same graph as you did. maybe you should ask the fella who marked you question.
 
I think the required answer is a straight line segment from the point (-1,-2) to the point (1,2)
 
if you look at the scanned image, SGT, the format implies that it ought to be ceiling(0.5x) that is plotted, not 0.5x, i think, though it is a little vague,
 
that symbol is the greatest integer function.
 
OK, I had not understood the meaning of the brackets. I think the solution is in the attached picture.
 
That is also not correct since 0.5*2=1, and ceiling(1) is 1, not two as your diagram shows.
 
matt grime said:
That is also not correct since 0.5*2=1, and ceiling(1) is 1, not two as your diagram shows.

My mistake. I was plotting y =[x], instead of y = [0.5x]. If the brackets really mean ceiling, your solution seems correct.
 
  • #10
UrbanXrisis said:
Why did I get this Math Question Wrong?

http://home.earthlink.net/~urban-xrisis/IMG_0373.jpg

I notice you have "open circles" at the left endpoint of each interval. Did you mean by that (or did whoever marked you wrong interpret that as) that point was not included in the interval? Since "ceiling" of x is the smallest integer greater than or equal to x, the left endpoint of each interval is included in the interval, but the right endpoint is not.
 
Last edited by a moderator:

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