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mathmath333

  • one year ago

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  1. mathmath333
    • one year ago
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    any short way to solve this . \(\large \color{black}{\begin{align} \left|\dfrac{x^2-5x+4}{x^2-4}\right|\leq 1\hspace{.33em}\\~\\ \end{align}}\)

  2. ganeshie8
    • one year ago
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    \(\large \left|\dfrac{x^2-5x+4}{x^2-4}\right| = \left|\dfrac{(x^2-4)-5x+8}{x^2-4}\right| = \left|1+\dfrac{-5x+8}{x^2-4}\right|\) For this to be \(\le 1\), clearly we must have \[-2\lt\dfrac{-5x+8}{x^2-4}\lt 0\]

  3. mathmath333
    • one year ago
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    u mean \(\large \color{black}{\begin{align} -2\leq\dfrac{-5x+8}{x^2-4}\leq 0\hspace{.33em}\\~\\ \end{align}}\) ?

  4. mathmath333
    • one year ago
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    i am also confused on how to further solve this . \(\large \color{black}{\begin{align} -2\leq\dfrac{-5x+8}{x^2-4}\leq 0\hspace{.33em}\\~\\ \end{align}}\)

  5. ganeshie8
    • one year ago
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    Ahh yes, consider two cases : Case1 : \(x^2-4\gt 0\) multiply \(x^2-4\) through out and get \[-2(x^2-4 )\le -5x+8 \le 0 \\~\\\implies -2x^2 \le -5x \le -8 \\~\\\implies 2x^2\ge 5x\ge 8 \\~\\\implies x\ge \frac{5}{2} \land x\ge \frac{8}{5}\\~\\\implies x\ge \frac{5}{2} \]

  6. ganeshie8
    • one year ago
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    similarly you can work the other case i don't like this method yeah too boring

  7. UsukiDoll
    • one year ago
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    \[\large \color{black}{\begin{align} \left|\dfrac{x^2-5x+4}{x^2-4}\right|\leq 1\hspace{.33em}\\~\\ \end{align}}\] Since we have the absolute value, we need to consider two cases. One when we have an all positive problem like this \[\frac{x^2-5x+4}{x^2-4} \leq 1 \] or \[-(\frac{x^2-5x+4}{x^2-4}) \leq 1 \] I'm going to try the all positive case \[\frac{x^2-5x+4}{x^2-4} \leq 1 \] so I would distribute the \[x^2-4 \] to the other side \[x^2-5x+4 \leq 1(x^2-4)\] \[x^2-5x+4 \leq x^2-4 \] \[x^2-5x+4 -x^2+4 \leq 0\] (and then put everything on the left... combine like terms) \[x^2-x^2-5x+4 +4 \leq 0\] \[-5x+8 \leq 0\] (simplify and divide. since we have a negative number, the sign switches from \[\leq \] to \[\geq \] \[-5x\leq -8\] \[x\geq \frac{8}{5}\]

  8. UsukiDoll
    • one year ago
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    there has got to be a way to make Latex nicer. this is ugly :P

  9. mathmath333
    • one year ago
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    the above needs to consider this two cases also \(\dfrac{x^2-5x+4}{x^2-4}\geq 0,\ \ \dfrac{x^2-5x+4}{x^2-4}< 0\)

  10. UsukiDoll
    • one year ago
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    I said I just picked one case :P I'm aware that there are two.

  11. mathmath333
    • one year ago
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    is there a way to transform the question in to this. \(\large \color{black}{\begin{align} \left|\dfrac{x^2-5x+4}{x^2-4}+\color{black}{constant}\right|\leq \color{red}{0}\hspace{.33em}\\~\\ \end{align}}\)

  12. UsukiDoll
    • one year ago
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    maybe subtract that 1 on both sides? But I have never done it, so I don't know if it's a legal math move.

  13. mathmath333
    • one year ago
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    i m not saying substract \(1\) lol

  14. UsukiDoll
    • one year ago
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    \[\frac{-x^2+5x-4}{x^2-4} \leq 1\] \[-x^2+5x-4 \leq 1(x^2-4)\] \[-x^2+5x-4 \leq x^2-4\] \[-x^2-x^2+5x-4+4 \leq 0\] \[-2x^2+5x\leq 0\] \[x(-2x+5)\leq 0\] x would be 0... blah don't want that case \[-2x+5 \leq 0 \] \[-2x \leq -5 \] \[x\geq \frac{5}{2} \] Looks like there is no faster way of doing this. You just have to use the absolute value rules which is consider the cases where we have an all positive situation and one where the negative sign is being distributed.

  15. anonymous
    • one year ago
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    Why you have chosen 1 to subtract @UsukiDoll ?

  16. UsukiDoll
    • one year ago
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    We have two cases thanks to the absolute value remember we either have all positive or we have a negative sign attached to the problem and have to distribute it and then do the same process as above. @ganeshie8 had the same answers I have.

  17. UsukiDoll
    • one year ago
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    \(\color{blue}{\text{Originally Posted by}}\) @waterineyes Why you have chosen 1 to subtract @UsukiDoll ? \(\color{blue}{\text{End of Quote}}\) didn't do it.. just in case that move didn't make sense :P

  18. anonymous
    • one year ago
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    Which move?

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