Absolute Value Inequality (another)












2












$begingroup$



Solve the following inequality



$$|a-2| > |a+4|$$




Here I separated it into cases as shown




$a<-4$




$$-(a-2) > -(a+4) implies 2-a>-a-4 implies 0>-6$$



Always true, so we get $mathbb{R} cap (-infty , -4) = (-infty ,-4)$




$-4<a<2$




$$-(a-2)>a+4 implies 2-a>a+4 implies a<-1$$



Taking interception $(-4,2)$ $cap $ $(-infty,-1)$




$a>2$




$$a-2 > a+4 implies -2>4 $$



Always false, so no solution from there. Finally, I checked end points and noticed that they do not work in this inequality. However, I do not know how to proceed further. Could you assist me?



Regards










share|cite|improve this question











$endgroup$












  • $begingroup$
    With $;a=4;$ your inequality is $$2=|4-2|>|4+4|=8...text{you still think this is true?}$$
    $endgroup$
    – DonAntonio
    Jan 13 at 13:18






  • 1




    $begingroup$
    @DonAntonio Not really, thanks for pointing out.
    $endgroup$
    – Enzo
    Jan 13 at 13:19
















2












$begingroup$



Solve the following inequality



$$|a-2| > |a+4|$$




Here I separated it into cases as shown




$a<-4$




$$-(a-2) > -(a+4) implies 2-a>-a-4 implies 0>-6$$



Always true, so we get $mathbb{R} cap (-infty , -4) = (-infty ,-4)$




$-4<a<2$




$$-(a-2)>a+4 implies 2-a>a+4 implies a<-1$$



Taking interception $(-4,2)$ $cap $ $(-infty,-1)$




$a>2$




$$a-2 > a+4 implies -2>4 $$



Always false, so no solution from there. Finally, I checked end points and noticed that they do not work in this inequality. However, I do not know how to proceed further. Could you assist me?



Regards










share|cite|improve this question











$endgroup$












  • $begingroup$
    With $;a=4;$ your inequality is $$2=|4-2|>|4+4|=8...text{you still think this is true?}$$
    $endgroup$
    – DonAntonio
    Jan 13 at 13:18






  • 1




    $begingroup$
    @DonAntonio Not really, thanks for pointing out.
    $endgroup$
    – Enzo
    Jan 13 at 13:19














2












2








2





$begingroup$



Solve the following inequality



$$|a-2| > |a+4|$$




Here I separated it into cases as shown




$a<-4$




$$-(a-2) > -(a+4) implies 2-a>-a-4 implies 0>-6$$



Always true, so we get $mathbb{R} cap (-infty , -4) = (-infty ,-4)$




$-4<a<2$




$$-(a-2)>a+4 implies 2-a>a+4 implies a<-1$$



Taking interception $(-4,2)$ $cap $ $(-infty,-1)$




$a>2$




$$a-2 > a+4 implies -2>4 $$



Always false, so no solution from there. Finally, I checked end points and noticed that they do not work in this inequality. However, I do not know how to proceed further. Could you assist me?



Regards










share|cite|improve this question











$endgroup$





Solve the following inequality



$$|a-2| > |a+4|$$




Here I separated it into cases as shown




$a<-4$




$$-(a-2) > -(a+4) implies 2-a>-a-4 implies 0>-6$$



Always true, so we get $mathbb{R} cap (-infty , -4) = (-infty ,-4)$




$-4<a<2$




$$-(a-2)>a+4 implies 2-a>a+4 implies a<-1$$



Taking interception $(-4,2)$ $cap $ $(-infty,-1)$




$a>2$




$$a-2 > a+4 implies -2>4 $$



Always false, so no solution from there. Finally, I checked end points and noticed that they do not work in this inequality. However, I do not know how to proceed further. Could you assist me?



Regards







inequality






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Jan 13 at 13:34









Ethan Bolker

43.1k551114




43.1k551114










asked Jan 13 at 13:16









EnzoEnzo

19917




19917












  • $begingroup$
    With $;a=4;$ your inequality is $$2=|4-2|>|4+4|=8...text{you still think this is true?}$$
    $endgroup$
    – DonAntonio
    Jan 13 at 13:18






  • 1




    $begingroup$
    @DonAntonio Not really, thanks for pointing out.
    $endgroup$
    – Enzo
    Jan 13 at 13:19


















  • $begingroup$
    With $;a=4;$ your inequality is $$2=|4-2|>|4+4|=8...text{you still think this is true?}$$
    $endgroup$
    – DonAntonio
    Jan 13 at 13:18






  • 1




    $begingroup$
    @DonAntonio Not really, thanks for pointing out.
    $endgroup$
    – Enzo
    Jan 13 at 13:19
















$begingroup$
With $;a=4;$ your inequality is $$2=|4-2|>|4+4|=8...text{you still think this is true?}$$
$endgroup$
– DonAntonio
Jan 13 at 13:18




$begingroup$
With $;a=4;$ your inequality is $$2=|4-2|>|4+4|=8...text{you still think this is true?}$$
$endgroup$
– DonAntonio
Jan 13 at 13:18




1




1




$begingroup$
@DonAntonio Not really, thanks for pointing out.
$endgroup$
– Enzo
Jan 13 at 13:19




$begingroup$
@DonAntonio Not really, thanks for pointing out.
$endgroup$
– Enzo
Jan 13 at 13:19










4 Answers
4






active

oldest

votes


















2












$begingroup$

As commented, $;a=4;$ doesn't really fits in the inequality. You can now put your solution set as



$$(-infty,-4)cupleft((-4,-2)cap(-infty,-1)right)=(-infty,-4)cup(-4,-1)=(-infty,-1)setminus{-4}$$






share|cite|improve this answer









$endgroup$













  • $begingroup$
    What does this mathematical symbol mean ?
    $endgroup$
    – Enzo
    Jan 13 at 13:23












  • $begingroup$
    Set difference. Sometimes it is also used $;A-B;$ ... A simple minus sign.
    $endgroup$
    – DonAntonio
    Jan 13 at 13:23










  • $begingroup$
    The right answer seems to be $(-infty, -1)$ according to my textbook. Do we get it from your final interval?:
    $endgroup$
    – Enzo
    Jan 13 at 13:24












  • $begingroup$
    That is correct, @Enzo . Your solution didn't even take into account $;a=-4;$ (perhaps you should have done this in the first case). That you have an inequality < or > doesn't mean you must take your cases in the same way
    $endgroup$
    – DonAntonio
    Jan 13 at 13:34





















2












$begingroup$

If you interpret the absolute values in terms of distance, it is immediate:



$|a-2|>|a+4|$ means $a$ is nearer to $-4$ than to $2$, so it is less than the arithmetic mean of $2$ and $-4$:
$$a<frac{2-4}2=-1$$



Other method:
begin{align}
|a-2|>|a+4|&iff(a-2)^2>(a+4)^2 \
&iff a^2-4a+4>a^2+8a+16\
&iff 12a+12<0iff a<-1.
end{align}






share|cite|improve this answer











$endgroup$





















    1












    $begingroup$

    You have to distinguish the following cases:
    $$xgeq 2$$ then we get $$x-2>x+4$$
    $$-4le x<2$$ then we get $$x-2>-x+4$$
    $$x<-4$$ then we have $$-x+2>-x-4$$






    share|cite|improve this answer









    $endgroup$





















      1












      $begingroup$

      $|(a+1)-3|>|(a+1)+3|;$



      $x:=a+1$;



      $|x-(+3)| >|x-(-3)|;$



      Real number line :



      Distance from a point $x$ to $(+3)$ is bigger than from $x$
      to $(-3)$, i.e. $x<0.$



      (Note : At $x=0$ both distances are equal, for $x <0$, $x$ is to the left of $0$ , closer to $(-3)$ ).



      $x= a+1<0$, $a<-1$.






      share|cite|improve this answer









      $endgroup$













        Your Answer





        StackExchange.ifUsing("editor", function () {
        return StackExchange.using("mathjaxEditing", function () {
        StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
        StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
        });
        });
        }, "mathjax-editing");

        StackExchange.ready(function() {
        var channelOptions = {
        tags: "".split(" "),
        id: "69"
        };
        initTagRenderer("".split(" "), "".split(" "), channelOptions);

        StackExchange.using("externalEditor", function() {
        // Have to fire editor after snippets, if snippets enabled
        if (StackExchange.settings.snippets.snippetsEnabled) {
        StackExchange.using("snippets", function() {
        createEditor();
        });
        }
        else {
        createEditor();
        }
        });

        function createEditor() {
        StackExchange.prepareEditor({
        heartbeatType: 'answer',
        autoActivateHeartbeat: false,
        convertImagesToLinks: true,
        noModals: true,
        showLowRepImageUploadWarning: true,
        reputationToPostImages: 10,
        bindNavPrevention: true,
        postfix: "",
        imageUploader: {
        brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
        contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
        allowUrls: true
        },
        noCode: true, onDemand: true,
        discardSelector: ".discard-answer"
        ,immediatelyShowMarkdownHelp:true
        });


        }
        });














        draft saved

        draft discarded


















        StackExchange.ready(
        function () {
        StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3071997%2fabsolute-value-inequality-another%23new-answer', 'question_page');
        }
        );

        Post as a guest















        Required, but never shown

























        4 Answers
        4






        active

        oldest

        votes








        4 Answers
        4






        active

        oldest

        votes









        active

        oldest

        votes






        active

        oldest

        votes









        2












        $begingroup$

        As commented, $;a=4;$ doesn't really fits in the inequality. You can now put your solution set as



        $$(-infty,-4)cupleft((-4,-2)cap(-infty,-1)right)=(-infty,-4)cup(-4,-1)=(-infty,-1)setminus{-4}$$






        share|cite|improve this answer









        $endgroup$













        • $begingroup$
          What does this mathematical symbol mean ?
          $endgroup$
          – Enzo
          Jan 13 at 13:23












        • $begingroup$
          Set difference. Sometimes it is also used $;A-B;$ ... A simple minus sign.
          $endgroup$
          – DonAntonio
          Jan 13 at 13:23










        • $begingroup$
          The right answer seems to be $(-infty, -1)$ according to my textbook. Do we get it from your final interval?:
          $endgroup$
          – Enzo
          Jan 13 at 13:24












        • $begingroup$
          That is correct, @Enzo . Your solution didn't even take into account $;a=-4;$ (perhaps you should have done this in the first case). That you have an inequality < or > doesn't mean you must take your cases in the same way
          $endgroup$
          – DonAntonio
          Jan 13 at 13:34


















        2












        $begingroup$

        As commented, $;a=4;$ doesn't really fits in the inequality. You can now put your solution set as



        $$(-infty,-4)cupleft((-4,-2)cap(-infty,-1)right)=(-infty,-4)cup(-4,-1)=(-infty,-1)setminus{-4}$$






        share|cite|improve this answer









        $endgroup$













        • $begingroup$
          What does this mathematical symbol mean ?
          $endgroup$
          – Enzo
          Jan 13 at 13:23












        • $begingroup$
          Set difference. Sometimes it is also used $;A-B;$ ... A simple minus sign.
          $endgroup$
          – DonAntonio
          Jan 13 at 13:23










        • $begingroup$
          The right answer seems to be $(-infty, -1)$ according to my textbook. Do we get it from your final interval?:
          $endgroup$
          – Enzo
          Jan 13 at 13:24












        • $begingroup$
          That is correct, @Enzo . Your solution didn't even take into account $;a=-4;$ (perhaps you should have done this in the first case). That you have an inequality < or > doesn't mean you must take your cases in the same way
          $endgroup$
          – DonAntonio
          Jan 13 at 13:34
















        2












        2








        2





        $begingroup$

        As commented, $;a=4;$ doesn't really fits in the inequality. You can now put your solution set as



        $$(-infty,-4)cupleft((-4,-2)cap(-infty,-1)right)=(-infty,-4)cup(-4,-1)=(-infty,-1)setminus{-4}$$






        share|cite|improve this answer









        $endgroup$



        As commented, $;a=4;$ doesn't really fits in the inequality. You can now put your solution set as



        $$(-infty,-4)cupleft((-4,-2)cap(-infty,-1)right)=(-infty,-4)cup(-4,-1)=(-infty,-1)setminus{-4}$$







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 13 at 13:22









        DonAntonioDonAntonio

        178k1494230




        178k1494230












        • $begingroup$
          What does this mathematical symbol mean ?
          $endgroup$
          – Enzo
          Jan 13 at 13:23












        • $begingroup$
          Set difference. Sometimes it is also used $;A-B;$ ... A simple minus sign.
          $endgroup$
          – DonAntonio
          Jan 13 at 13:23










        • $begingroup$
          The right answer seems to be $(-infty, -1)$ according to my textbook. Do we get it from your final interval?:
          $endgroup$
          – Enzo
          Jan 13 at 13:24












        • $begingroup$
          That is correct, @Enzo . Your solution didn't even take into account $;a=-4;$ (perhaps you should have done this in the first case). That you have an inequality < or > doesn't mean you must take your cases in the same way
          $endgroup$
          – DonAntonio
          Jan 13 at 13:34




















        • $begingroup$
          What does this mathematical symbol mean ?
          $endgroup$
          – Enzo
          Jan 13 at 13:23












        • $begingroup$
          Set difference. Sometimes it is also used $;A-B;$ ... A simple minus sign.
          $endgroup$
          – DonAntonio
          Jan 13 at 13:23










        • $begingroup$
          The right answer seems to be $(-infty, -1)$ according to my textbook. Do we get it from your final interval?:
          $endgroup$
          – Enzo
          Jan 13 at 13:24












        • $begingroup$
          That is correct, @Enzo . Your solution didn't even take into account $;a=-4;$ (perhaps you should have done this in the first case). That you have an inequality < or > doesn't mean you must take your cases in the same way
          $endgroup$
          – DonAntonio
          Jan 13 at 13:34


















        $begingroup$
        What does this mathematical symbol mean ?
        $endgroup$
        – Enzo
        Jan 13 at 13:23






        $begingroup$
        What does this mathematical symbol mean ?
        $endgroup$
        – Enzo
        Jan 13 at 13:23














        $begingroup$
        Set difference. Sometimes it is also used $;A-B;$ ... A simple minus sign.
        $endgroup$
        – DonAntonio
        Jan 13 at 13:23




        $begingroup$
        Set difference. Sometimes it is also used $;A-B;$ ... A simple minus sign.
        $endgroup$
        – DonAntonio
        Jan 13 at 13:23












        $begingroup$
        The right answer seems to be $(-infty, -1)$ according to my textbook. Do we get it from your final interval?:
        $endgroup$
        – Enzo
        Jan 13 at 13:24






        $begingroup$
        The right answer seems to be $(-infty, -1)$ according to my textbook. Do we get it from your final interval?:
        $endgroup$
        – Enzo
        Jan 13 at 13:24














        $begingroup$
        That is correct, @Enzo . Your solution didn't even take into account $;a=-4;$ (perhaps you should have done this in the first case). That you have an inequality < or > doesn't mean you must take your cases in the same way
        $endgroup$
        – DonAntonio
        Jan 13 at 13:34






        $begingroup$
        That is correct, @Enzo . Your solution didn't even take into account $;a=-4;$ (perhaps you should have done this in the first case). That you have an inequality < or > doesn't mean you must take your cases in the same way
        $endgroup$
        – DonAntonio
        Jan 13 at 13:34













        2












        $begingroup$

        If you interpret the absolute values in terms of distance, it is immediate:



        $|a-2|>|a+4|$ means $a$ is nearer to $-4$ than to $2$, so it is less than the arithmetic mean of $2$ and $-4$:
        $$a<frac{2-4}2=-1$$



        Other method:
        begin{align}
        |a-2|>|a+4|&iff(a-2)^2>(a+4)^2 \
        &iff a^2-4a+4>a^2+8a+16\
        &iff 12a+12<0iff a<-1.
        end{align}






        share|cite|improve this answer











        $endgroup$


















          2












          $begingroup$

          If you interpret the absolute values in terms of distance, it is immediate:



          $|a-2|>|a+4|$ means $a$ is nearer to $-4$ than to $2$, so it is less than the arithmetic mean of $2$ and $-4$:
          $$a<frac{2-4}2=-1$$



          Other method:
          begin{align}
          |a-2|>|a+4|&iff(a-2)^2>(a+4)^2 \
          &iff a^2-4a+4>a^2+8a+16\
          &iff 12a+12<0iff a<-1.
          end{align}






          share|cite|improve this answer











          $endgroup$
















            2












            2








            2





            $begingroup$

            If you interpret the absolute values in terms of distance, it is immediate:



            $|a-2|>|a+4|$ means $a$ is nearer to $-4$ than to $2$, so it is less than the arithmetic mean of $2$ and $-4$:
            $$a<frac{2-4}2=-1$$



            Other method:
            begin{align}
            |a-2|>|a+4|&iff(a-2)^2>(a+4)^2 \
            &iff a^2-4a+4>a^2+8a+16\
            &iff 12a+12<0iff a<-1.
            end{align}






            share|cite|improve this answer











            $endgroup$



            If you interpret the absolute values in terms of distance, it is immediate:



            $|a-2|>|a+4|$ means $a$ is nearer to $-4$ than to $2$, so it is less than the arithmetic mean of $2$ and $-4$:
            $$a<frac{2-4}2=-1$$



            Other method:
            begin{align}
            |a-2|>|a+4|&iff(a-2)^2>(a+4)^2 \
            &iff a^2-4a+4>a^2+8a+16\
            &iff 12a+12<0iff a<-1.
            end{align}







            share|cite|improve this answer














            share|cite|improve this answer



            share|cite|improve this answer








            edited Jan 13 at 13:51

























            answered Jan 13 at 13:42









            BernardBernard

            121k740116




            121k740116























                1












                $begingroup$

                You have to distinguish the following cases:
                $$xgeq 2$$ then we get $$x-2>x+4$$
                $$-4le x<2$$ then we get $$x-2>-x+4$$
                $$x<-4$$ then we have $$-x+2>-x-4$$






                share|cite|improve this answer









                $endgroup$


















                  1












                  $begingroup$

                  You have to distinguish the following cases:
                  $$xgeq 2$$ then we get $$x-2>x+4$$
                  $$-4le x<2$$ then we get $$x-2>-x+4$$
                  $$x<-4$$ then we have $$-x+2>-x-4$$






                  share|cite|improve this answer









                  $endgroup$
















                    1












                    1








                    1





                    $begingroup$

                    You have to distinguish the following cases:
                    $$xgeq 2$$ then we get $$x-2>x+4$$
                    $$-4le x<2$$ then we get $$x-2>-x+4$$
                    $$x<-4$$ then we have $$-x+2>-x-4$$






                    share|cite|improve this answer









                    $endgroup$



                    You have to distinguish the following cases:
                    $$xgeq 2$$ then we get $$x-2>x+4$$
                    $$-4le x<2$$ then we get $$x-2>-x+4$$
                    $$x<-4$$ then we have $$-x+2>-x-4$$







                    share|cite|improve this answer












                    share|cite|improve this answer



                    share|cite|improve this answer










                    answered Jan 13 at 13:20









                    Dr. Sonnhard GraubnerDr. Sonnhard Graubner

                    75.3k42865




                    75.3k42865























                        1












                        $begingroup$

                        $|(a+1)-3|>|(a+1)+3|;$



                        $x:=a+1$;



                        $|x-(+3)| >|x-(-3)|;$



                        Real number line :



                        Distance from a point $x$ to $(+3)$ is bigger than from $x$
                        to $(-3)$, i.e. $x<0.$



                        (Note : At $x=0$ both distances are equal, for $x <0$, $x$ is to the left of $0$ , closer to $(-3)$ ).



                        $x= a+1<0$, $a<-1$.






                        share|cite|improve this answer









                        $endgroup$


















                          1












                          $begingroup$

                          $|(a+1)-3|>|(a+1)+3|;$



                          $x:=a+1$;



                          $|x-(+3)| >|x-(-3)|;$



                          Real number line :



                          Distance from a point $x$ to $(+3)$ is bigger than from $x$
                          to $(-3)$, i.e. $x<0.$



                          (Note : At $x=0$ both distances are equal, for $x <0$, $x$ is to the left of $0$ , closer to $(-3)$ ).



                          $x= a+1<0$, $a<-1$.






                          share|cite|improve this answer









                          $endgroup$
















                            1












                            1








                            1





                            $begingroup$

                            $|(a+1)-3|>|(a+1)+3|;$



                            $x:=a+1$;



                            $|x-(+3)| >|x-(-3)|;$



                            Real number line :



                            Distance from a point $x$ to $(+3)$ is bigger than from $x$
                            to $(-3)$, i.e. $x<0.$



                            (Note : At $x=0$ both distances are equal, for $x <0$, $x$ is to the left of $0$ , closer to $(-3)$ ).



                            $x= a+1<0$, $a<-1$.






                            share|cite|improve this answer









                            $endgroup$



                            $|(a+1)-3|>|(a+1)+3|;$



                            $x:=a+1$;



                            $|x-(+3)| >|x-(-3)|;$



                            Real number line :



                            Distance from a point $x$ to $(+3)$ is bigger than from $x$
                            to $(-3)$, i.e. $x<0.$



                            (Note : At $x=0$ both distances are equal, for $x <0$, $x$ is to the left of $0$ , closer to $(-3)$ ).



                            $x= a+1<0$, $a<-1$.







                            share|cite|improve this answer












                            share|cite|improve this answer



                            share|cite|improve this answer










                            answered Jan 13 at 16:14









                            Peter SzilasPeter Szilas

                            11.3k2822




                            11.3k2822






























                                draft saved

                                draft discarded




















































                                Thanks for contributing an answer to Mathematics Stack Exchange!


                                • Please be sure to answer the question. Provide details and share your research!

                                But avoid



                                • Asking for help, clarification, or responding to other answers.

                                • Making statements based on opinion; back them up with references or personal experience.


                                Use MathJax to format equations. MathJax reference.


                                To learn more, see our tips on writing great answers.




                                draft saved


                                draft discarded














                                StackExchange.ready(
                                function () {
                                StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3071997%2fabsolute-value-inequality-another%23new-answer', 'question_page');
                                }
                                );

                                Post as a guest















                                Required, but never shown





















































                                Required, but never shown














                                Required, but never shown












                                Required, but never shown







                                Required, but never shown

































                                Required, but never shown














                                Required, but never shown












                                Required, but never shown







                                Required, but never shown







                                Popular posts from this blog

                                android studio warns about leanback feature tag usage required on manifest while using Unity exported app?

                                SQL update select statement

                                WPF add header to Image with URL pettitions [duplicate]