Wrong Answer From Calculator for x^2-1 (all over) x+4

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Discussion Overview

The discussion revolves around evaluating the function f(x) = (x^2 - 1) / (x + 4) at the point x = 2a - 1. Participants are comparing their results and addressing discrepancies between their calculations and those produced by calculators. The scope includes mathematical reasoning and clarification of LaTeX formatting for expressions.

Discussion Character

  • Mathematical reasoning
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant reports obtaining f(2a-1) = 4a^2 / (2a + 3) while their calculator gives a different result of ((2a-1)^2 - 1) / (2a + 3).
  • Another participant humorously notes a discrepancy in variable usage, pointing out the need for "a" instead of "x".
  • Clarifications are made regarding the expansion of (2a - 1)^2, leading to the expression 4a^2 - 4a + 1, and the subsequent simplification to 4a^2 - 4a.
  • Participants discuss the correct LaTeX formatting for mathematical expressions, highlighting the need for [tex] at the beginning of the code.
  • One participant questions the origin of the +1 in the expansion and discusses the cancellation of terms in their calculations.
  • A later reply confirms that the +1 does indeed come from the expansion of (2a - 1)^2, but emphasizes that the earlier expression of 4a^2 is not accurate.

Areas of Agreement / Disagreement

Participants express differing results and interpretations of the calculations, indicating that there is no consensus on the correct answer or the steps leading to it. The discussion remains unresolved regarding the discrepancies in their findings.

Contextual Notes

Participants have not fully resolved the assumptions behind their calculations, particularly regarding the expansion and simplification of polynomial expressions. There are also unresolved questions about the proper use of LaTeX formatting.

alliecr
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I am not getting the answer that my calculator is giving me for the following:

Find the following values for x^2-1 (all over) x+4

f(2a-1)

I am getting 4a^2 (all over) 2a+3 for my final answer and my calculator is getting (2a-1)^2-1 (all over) 2a+3.

What did I do wrong? Also, how do you work the math latex references?
these:
[x[2]^{}[/tex]-1]\frac{}{}[/x+4]
 
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funny. I got x-4+(15)/(x+4)
 
Hydrargyrum said:
funny. I got x-4+(15)/(x+4)
Since the answer must have "a" rather that "x" that's not particularly funny!

alliecr said:
I am not getting the answer that my calculator is giving me for the following:

Find the following values for x^2-1 (all over) x+4

f(2a-1)

I am getting 4a^2 (all over) 2a+3 for my final answer and my calculator is getting (2a-1)^2-1 (all over) 2a+3.
Okay, if x= 2a- 1, then x2= (2a-1)2= 4a2- 4a+ 1 so x2- 1= 4a2- 4a. How did you get "4a2"? Also x+ 4= (2a-1)+ 4= 2a+ 3. You have
[tex]\frac{4a^2- 4a+ 1}{2a+ 3}[/ite]<br /> <br /> <blockquote data-attributes="" data-quote="" data-source="" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> What did I do wrong? Also, how do you work the math latex references?<br /> these:<br /> [x[2]^{} </div> </div> </blockquote>[/tex]
-1]\frac{}{}[/x+4]
The [/tex] only ends a latex code. You need [tex]in front. Did you know that you can see the code for a latex formula by clicking on it?[/tex]
 
HallsofIvy said:
Since the answer must have "a" rather that "x" that's not particularly funny!


Okay, if x= 2a- 1, then x2= (2a-1)2= 4a2- 4a+ 1 so x2- 1= 4a2- 4a. How did you get "4a2"? Also x+ 4= (2a-1)+ 4= 2a+ 3. You have
[tex]\frac{4a^2- 4a+ 1}{2a+ 3}[/ite]<br /> <br /> <br /> The[/tex] only ends a latex code. You need [tex]in front. Did you know that you can see the code for a latex formula by clicking on it?[/tex]
[tex] <br /> Where does the+1 come from? I had this before I got my answer: [tex]4a^{2}-2a-2a+1-1...the ones would cancel out right?[/tex][/tex]
 
[tex]f(x) = \frac{x^2-1}{x+4}[/tex]
If x = 2a - 1 then we have:
[tex]f(2a-1) = \frac{(2a-1)^2-1}{(2a-1) + 4} = \frac{(4a^2 - 4a +1) -1}{2a +3} = \frac{4a^2 - 4a}{2a +3}[/tex]

You could end here or factor out the 4a on the numerator if you really wanted to.
[tex]\frac{4a(a - 1)}{2a+3}[/tex]
 
alliecr said:
Where does the+1 come from? I had this before I got my answer: [tex]4a^{2}-2a-2a+1-1...the ones would cancel out right?[/tex]
[tex] Yes, and I showed that it did. I said (2a-1)<sup>2</sup>= 4a<sup>2</sup>- 4a+ 1 so (2a-1)<sup>2</sup>+ 1= 4a<sup>2</sup>- 4a just as you have now and just as I had before. But 4a<sup>2</sup>- 4a is NOT the 4a<sup>2</sup> you had before![/tex]
 

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