Pulling out -1 from denominator?

  • Context: High School 
  • Thread starter Thread starter bob1182006
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Discussion Overview

The discussion revolves around the manipulation of fractions, specifically the concept of factoring out -1 from the denominator in expressions. Participants explore whether the equation \(\frac{a}{b-c}=-1\frac{a}{c-b}\) holds true and discuss related mathematical properties.

Discussion Character

  • Mathematical reasoning

Main Points Raised

  • One participant questions the validity of the expression \(\frac{a}{b-c}=-1\frac{a}{c-b}\) and seeks clarification on whether it is always true.
  • Another participant asserts that the manipulation is obvious, referencing the relationship \((-x)/y=x/(-y)=-(x/y).
  • A third participant agrees with the initial claim, stating it is a special case of the property \(\frac{1}{ab}=\frac{1}{a}\cdot\frac{1}{b}\).
  • A participant expresses gratitude for the clarification and notes a lack of coverage on this topic in their previous education.
  • One participant suggests proving basic statements about fractions, such as \(\frac{1}{1}=1\) and \(\frac{1}{(-1)}=(-1)\cdot\frac{1}{1}=(-1)\).

Areas of Agreement / Disagreement

Participants generally agree on the validity of the manipulation, but there is no explicit consensus on the broader implications or applications of this property.

Contextual Notes

Some assumptions about the variables and their domains are not explicitly stated, and the discussion does not resolve potential limitations or conditions under which the manipulation may apply.

bob1182006
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I know this might seem trivial but I've never had a teacher cover this even though I've had the whole "factor out -1 from numerator " class.

I was thinking of the cases but I haven't found a contradiction to:

[tex]\frac{a}{b-c}=-1\frac{a}{c-b}[/tex]

so is this always true?
 
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Obviously. After all (-x)/y=x/(-y)=-(x/y).
 
It's true. It's a special case of

[tex]\frac{1}{ab}=\frac1a\cdot\frac1b[/tex]
 
thanks
I've always wondered about that...
for some reason no teacher I've had has ever done that manipulation.
 
You might try to prove the following statements:
[tex]\frac{1}{1}=1, \frac{1}{(-1)}=(-1)*\frac{1}{1}=(-1)[/tex]
 

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