When find LCD for a rational expressions.

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Discussion Overview

The discussion revolves around finding the Lowest Common Denominator (LCD) for rational expressions, specifically focusing on the denominators x² - 4 and x - 2. Participants explore the methodology for determining the LCD, including factoring and identifying common terms.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that the LCD for the denominators x² - 4 and x - 2 is simply x - 2, questioning the necessity of including all factors.
  • Another participant argues that the LCD must be a common multiple of the original denominators, using the analogy of finding the lowest common multiple of numbers.
  • It is noted that x² - 4 factors into (x - 2)(x + 2), which leads to a discussion about including all distinct factors when determining the LCD.
  • Some participants express confusion about the process, asking for clarification on whether to multiply all factors or just the common ones.
  • There is a point made that simply multiplying the denominators may not yield the correct LCD unless the polynomials are coprime.
  • One participant emphasizes the importance of understanding why the LCD is x² - 4, rather than just providing the answer.

Areas of Agreement / Disagreement

Participants do not reach consensus on the correct approach to finding the LCD, with differing opinions on whether to include all factors or just the common ones. The discussion remains unresolved regarding the methodology for determining the LCD.

Contextual Notes

Participants express uncertainty about the definitions of common multiples and the implications of factoring in the context of rational expressions. There are unresolved questions about the correct application of these concepts.

DLxX
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Ok I have to find the Lowest Common Denominator for 3 ration expressions.
I don't think the numerators are important so Ill just leave them out. The denominators are

x^2 - 4 and x -2 I got the LCD as x-2. correct?

When finding the LCD in expressions like this you just have to factor and pick the term that they both have in common right?
 
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Nope,u have to pick just that:the lowest common denominator.Think of the numbers:what is the lowest common multiple of 6 and 3...?Is it 3??

Daniel.
 
Well the first one comes out to (x-2) and (x+2) while the 2nd one just stays as (x-2). So isn't the only CD they have (x-2)?
 
No,because the common denominator has to be a common multiple of the "old" denominators...That's why i gave the example with the numbers...Instead of #,you have polynimials...

Daniel.
 
Would you mind just giving me the answer for the one I mentioned? I have 3 more problems just like it and right now I am seriously not getting it.
 
It would really matter for you to know/understand why the answers is the one that it is,namely x^{2}-4.

Daniel.
 
Ok I think I get it now. You take x-2 from the first one and x-2 from the 2nd one and multiply them right? But wouldn't that end up x^2 -4x + 4? Why do I take the x+2 from the first one?

EDIT: I take all the DIFFERENT factors right? So that they each get a part?
 
Nope,it has to be the smallest common denominator,as i said the smalles common MULTIPLE OF THE 2 DENOMINATOS.The smallest one for x^{2}-4 is x^{2}-4 and that's that...

That simple multiplication between the denominators would be valid if the 2 polynomials would be prime one wrt another,which is not the case in here...

Daniel.
 
So I can essentially just multiply the 2 denominators of any problem like this and still get the correct answer? Or factor out the 2 denominators and multiply all the factors with each other, crossing out all the factors that were in both?
 
  • #10
Yes,you finally got it...That "crossing out" doesn't mean eliminating,just "counting" only once in the product,okay?
In your case,you'd have to count "x-2" only once.

Daniel.
 

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