How can the absolute value of x be negative?

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Homework Help Overview

The discussion revolves around the concept of absolute value in mathematics, specifically addressing the question of how the absolute value of a number can be perceived as negative in certain contexts. Participants are examining the definitions and implications of absolute value as presented in a textbook, particularly in relation to the triangle inequality.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are exploring the definition of absolute value, questioning the conditions under which it is considered negative. There is a focus on the implications of assuming different values for x, particularly when x is negative.

Discussion Status

The discussion is progressing with participants clarifying their understanding of absolute value. Some have offered insights that help others grasp the relationship between negative values and their absolute counterparts. There is a recognition of the need to reconcile definitions with examples, indicating a productive exploration of the topic.

Contextual Notes

Participants are grappling with the definitions provided in the textbook, which may not align with their initial interpretations. The discussion highlights the importance of understanding the conditions under which absolute values are defined and the potential for confusion in their application.

Joseph1739
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Homework Statement


http://imgur.com/RlIdmFh
http://imgur.com/3dnLK3m

Homework Equations


|x| = -x?

The Attempt at a Solution


I'm trying to make sense of this definition in my book because they are trying to prove the triangle inequality(second link), yet it keeps saying that the absolute value of a number is negative.
 
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Your interpretation is only true if you're assuming x>0. What if x itself is negative?
 
vela said:
Your interpretation is only true if you're assuming x>0. What if x itself is negative?
The absolute value would still be positive? Isn't the point of absolute value to obtain positive results only?
 
If ##x=-1##, what's ##-x## equal to?
 
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vela said:
If ##x=-1##, what's ##-x## equal to?
1. How does that explain the definition given though? It says |x| = -x if x<0. So by his definition, if I say x = -3, |x| = |-3| = -3.
 
vela said:
If ##x=-1##, what's ##-x## equal to?
Ohhh. I understand it now. |-3| = -(-3) = 3.
 
Yup, you got it.
 
A very straightforward definition.
If x is non-negative, then x is just x itself. If x is negative, what do you have to do to make it positive for certain? Put a minus in front, for two minuses give a + :)
 

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