Solve the inequality $frac{2}{x} > 3 x$ [closed]












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I've been slowly losing my mind on how to do this question, any help would be greatly appreciated.




Solve the inequality $$frac{2}{x} > 3 x.$$











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closed as off-topic by Xander Henderson, zz20s, Eevee Trainer, mrtaurho, Claude Leibovici Jan 14 at 7:08


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    Draw a picture!!!
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    – aidangallagher4
    Jan 14 at 0:04
















1












$begingroup$


I've been slowly losing my mind on how to do this question, any help would be greatly appreciated.




Solve the inequality $$frac{2}{x} > 3 x.$$











share|cite|improve this question











$endgroup$



closed as off-topic by Xander Henderson, zz20s, Eevee Trainer, mrtaurho, Claude Leibovici Jan 14 at 7:08


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Xander Henderson, zz20s, Eevee Trainer, mrtaurho, Claude Leibovici

If this question can be reworded to fit the rules in the help center, please edit the question.












  • 2




    $begingroup$
    Draw a picture!!!
    $endgroup$
    – aidangallagher4
    Jan 14 at 0:04














1












1








1





$begingroup$


I've been slowly losing my mind on how to do this question, any help would be greatly appreciated.




Solve the inequality $$frac{2}{x} > 3 x.$$











share|cite|improve this question











$endgroup$




I've been slowly losing my mind on how to do this question, any help would be greatly appreciated.




Solve the inequality $$frac{2}{x} > 3 x.$$








algebra-precalculus inequality






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edited Jan 14 at 0:04









Viktor Glombik

1,3802628




1,3802628










asked Jan 13 at 23:49









Nanji ChoNanji Cho

83




83




closed as off-topic by Xander Henderson, zz20s, Eevee Trainer, mrtaurho, Claude Leibovici Jan 14 at 7:08


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Xander Henderson, zz20s, Eevee Trainer, mrtaurho, Claude Leibovici

If this question can be reworded to fit the rules in the help center, please edit the question.







closed as off-topic by Xander Henderson, zz20s, Eevee Trainer, mrtaurho, Claude Leibovici Jan 14 at 7:08


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Xander Henderson, zz20s, Eevee Trainer, mrtaurho, Claude Leibovici

If this question can be reworded to fit the rules in the help center, please edit the question.








  • 2




    $begingroup$
    Draw a picture!!!
    $endgroup$
    – aidangallagher4
    Jan 14 at 0:04














  • 2




    $begingroup$
    Draw a picture!!!
    $endgroup$
    – aidangallagher4
    Jan 14 at 0:04








2




2




$begingroup$
Draw a picture!!!
$endgroup$
– aidangallagher4
Jan 14 at 0:04




$begingroup$
Draw a picture!!!
$endgroup$
– aidangallagher4
Jan 14 at 0:04










3 Answers
3






active

oldest

votes


















6












$begingroup$

To solve the equation
$$
frac{2}{x} > 3x
$$

we could multiply be $x$ to obtain
$$
2 > 3x^2.
$$

But you have to be careful!
If $x < 0$, the inequality is reversed.
In other words:
$$
frac{2}{x} > 3x
iff begin{cases}
2 < 3x^2 & x < 0 \
2 > 3x^2 & x > 0.
end{cases}
$$

Notice the equation isn't defined for $x = 0$, because you can't divide by $0$.



Case 1: $x > 0$.
Then we have
$$
2> 3x^2
iff x^2 < frac{2}{3}
iff x in left(- sqrt{ frac{2}{3}}, sqrt{ frac{2}{3}}right).
$$

But, since $x > 0$, our first solution interval is $I_1 := left(0, sqrt{ frac{2}{3}}right)$.



Case 2: $x < 0$.
Then we have
$$
2 < 3x^2
iff x^2 > frac{3}{2}
iff x > sqrt{frac{3}{2}} quad text{and} qquad x < -sqrt{frac{3}{2}}
$$

But again, since $x < 0$, our second (and final) solution interval is $I_2 := left(- infty, -sqrt{frac{3}{2}}right)$.



So our solution is $I_1 cup I_2 =left(- infty, -sqrt{frac{3}{2}}right) cup left(0, sqrt{ frac{2}{3}}right)$.






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$endgroup$





















    5












    $begingroup$

    We observe that necessarily $xneq 0$ whence we can rewrite the inequality as
    $$
    frac{2}{x}-3x>0ifffrac{2x-3x^3}{x^2}>0iff 2x-3x^3>0iff x(2-3x^2)>0
    $$

    which you can solve.






    share|cite|improve this answer











    $endgroup$





















      3












      $begingroup$

      Usually you're supposed to give some context and explain what you've tried so far. However, I will take your word that you have been "slowly losing" your mind and give an answer.



      Since this is a nonlinear inequality, there is no "cookie cutter" way to solve it. But you can get an idea of what to do by graphing $y_1=2/x$ and $y_2=3x$, and observing where $y_1>y_2$.



      See here for a graph with $y_1=2/x$ in red and $y_2=3x$ in blue. Where does the red curve lie above the blue curve?



      Well, you can see that there are two intersection points. But the red lies above the blue from $-infty$ up to the first intersection point, and then again from zero to the second intersection point.



      To find the intersection points, set $2/x=3x$ and solve.



      Can you write down the final answer?






      share|cite|improve this answer









      $endgroup$




















        3 Answers
        3






        active

        oldest

        votes








        3 Answers
        3






        active

        oldest

        votes









        active

        oldest

        votes






        active

        oldest

        votes









        6












        $begingroup$

        To solve the equation
        $$
        frac{2}{x} > 3x
        $$

        we could multiply be $x$ to obtain
        $$
        2 > 3x^2.
        $$

        But you have to be careful!
        If $x < 0$, the inequality is reversed.
        In other words:
        $$
        frac{2}{x} > 3x
        iff begin{cases}
        2 < 3x^2 & x < 0 \
        2 > 3x^2 & x > 0.
        end{cases}
        $$

        Notice the equation isn't defined for $x = 0$, because you can't divide by $0$.



        Case 1: $x > 0$.
        Then we have
        $$
        2> 3x^2
        iff x^2 < frac{2}{3}
        iff x in left(- sqrt{ frac{2}{3}}, sqrt{ frac{2}{3}}right).
        $$

        But, since $x > 0$, our first solution interval is $I_1 := left(0, sqrt{ frac{2}{3}}right)$.



        Case 2: $x < 0$.
        Then we have
        $$
        2 < 3x^2
        iff x^2 > frac{3}{2}
        iff x > sqrt{frac{3}{2}} quad text{and} qquad x < -sqrt{frac{3}{2}}
        $$

        But again, since $x < 0$, our second (and final) solution interval is $I_2 := left(- infty, -sqrt{frac{3}{2}}right)$.



        So our solution is $I_1 cup I_2 =left(- infty, -sqrt{frac{3}{2}}right) cup left(0, sqrt{ frac{2}{3}}right)$.






        share|cite|improve this answer











        $endgroup$


















          6












          $begingroup$

          To solve the equation
          $$
          frac{2}{x} > 3x
          $$

          we could multiply be $x$ to obtain
          $$
          2 > 3x^2.
          $$

          But you have to be careful!
          If $x < 0$, the inequality is reversed.
          In other words:
          $$
          frac{2}{x} > 3x
          iff begin{cases}
          2 < 3x^2 & x < 0 \
          2 > 3x^2 & x > 0.
          end{cases}
          $$

          Notice the equation isn't defined for $x = 0$, because you can't divide by $0$.



          Case 1: $x > 0$.
          Then we have
          $$
          2> 3x^2
          iff x^2 < frac{2}{3}
          iff x in left(- sqrt{ frac{2}{3}}, sqrt{ frac{2}{3}}right).
          $$

          But, since $x > 0$, our first solution interval is $I_1 := left(0, sqrt{ frac{2}{3}}right)$.



          Case 2: $x < 0$.
          Then we have
          $$
          2 < 3x^2
          iff x^2 > frac{3}{2}
          iff x > sqrt{frac{3}{2}} quad text{and} qquad x < -sqrt{frac{3}{2}}
          $$

          But again, since $x < 0$, our second (and final) solution interval is $I_2 := left(- infty, -sqrt{frac{3}{2}}right)$.



          So our solution is $I_1 cup I_2 =left(- infty, -sqrt{frac{3}{2}}right) cup left(0, sqrt{ frac{2}{3}}right)$.






          share|cite|improve this answer











          $endgroup$
















            6












            6








            6





            $begingroup$

            To solve the equation
            $$
            frac{2}{x} > 3x
            $$

            we could multiply be $x$ to obtain
            $$
            2 > 3x^2.
            $$

            But you have to be careful!
            If $x < 0$, the inequality is reversed.
            In other words:
            $$
            frac{2}{x} > 3x
            iff begin{cases}
            2 < 3x^2 & x < 0 \
            2 > 3x^2 & x > 0.
            end{cases}
            $$

            Notice the equation isn't defined for $x = 0$, because you can't divide by $0$.



            Case 1: $x > 0$.
            Then we have
            $$
            2> 3x^2
            iff x^2 < frac{2}{3}
            iff x in left(- sqrt{ frac{2}{3}}, sqrt{ frac{2}{3}}right).
            $$

            But, since $x > 0$, our first solution interval is $I_1 := left(0, sqrt{ frac{2}{3}}right)$.



            Case 2: $x < 0$.
            Then we have
            $$
            2 < 3x^2
            iff x^2 > frac{3}{2}
            iff x > sqrt{frac{3}{2}} quad text{and} qquad x < -sqrt{frac{3}{2}}
            $$

            But again, since $x < 0$, our second (and final) solution interval is $I_2 := left(- infty, -sqrt{frac{3}{2}}right)$.



            So our solution is $I_1 cup I_2 =left(- infty, -sqrt{frac{3}{2}}right) cup left(0, sqrt{ frac{2}{3}}right)$.






            share|cite|improve this answer











            $endgroup$



            To solve the equation
            $$
            frac{2}{x} > 3x
            $$

            we could multiply be $x$ to obtain
            $$
            2 > 3x^2.
            $$

            But you have to be careful!
            If $x < 0$, the inequality is reversed.
            In other words:
            $$
            frac{2}{x} > 3x
            iff begin{cases}
            2 < 3x^2 & x < 0 \
            2 > 3x^2 & x > 0.
            end{cases}
            $$

            Notice the equation isn't defined for $x = 0$, because you can't divide by $0$.



            Case 1: $x > 0$.
            Then we have
            $$
            2> 3x^2
            iff x^2 < frac{2}{3}
            iff x in left(- sqrt{ frac{2}{3}}, sqrt{ frac{2}{3}}right).
            $$

            But, since $x > 0$, our first solution interval is $I_1 := left(0, sqrt{ frac{2}{3}}right)$.



            Case 2: $x < 0$.
            Then we have
            $$
            2 < 3x^2
            iff x^2 > frac{3}{2}
            iff x > sqrt{frac{3}{2}} quad text{and} qquad x < -sqrt{frac{3}{2}}
            $$

            But again, since $x < 0$, our second (and final) solution interval is $I_2 := left(- infty, -sqrt{frac{3}{2}}right)$.



            So our solution is $I_1 cup I_2 =left(- infty, -sqrt{frac{3}{2}}right) cup left(0, sqrt{ frac{2}{3}}right)$.







            share|cite|improve this answer














            share|cite|improve this answer



            share|cite|improve this answer








            edited Jan 14 at 0:04

























            answered Jan 13 at 23:52









            Viktor GlombikViktor Glombik

            1,3802628




            1,3802628























                5












                $begingroup$

                We observe that necessarily $xneq 0$ whence we can rewrite the inequality as
                $$
                frac{2}{x}-3x>0ifffrac{2x-3x^3}{x^2}>0iff 2x-3x^3>0iff x(2-3x^2)>0
                $$

                which you can solve.






                share|cite|improve this answer











                $endgroup$


















                  5












                  $begingroup$

                  We observe that necessarily $xneq 0$ whence we can rewrite the inequality as
                  $$
                  frac{2}{x}-3x>0ifffrac{2x-3x^3}{x^2}>0iff 2x-3x^3>0iff x(2-3x^2)>0
                  $$

                  which you can solve.






                  share|cite|improve this answer











                  $endgroup$
















                    5












                    5








                    5





                    $begingroup$

                    We observe that necessarily $xneq 0$ whence we can rewrite the inequality as
                    $$
                    frac{2}{x}-3x>0ifffrac{2x-3x^3}{x^2}>0iff 2x-3x^3>0iff x(2-3x^2)>0
                    $$

                    which you can solve.






                    share|cite|improve this answer











                    $endgroup$



                    We observe that necessarily $xneq 0$ whence we can rewrite the inequality as
                    $$
                    frac{2}{x}-3x>0ifffrac{2x-3x^3}{x^2}>0iff 2x-3x^3>0iff x(2-3x^2)>0
                    $$

                    which you can solve.







                    share|cite|improve this answer














                    share|cite|improve this answer



                    share|cite|improve this answer








                    edited Jan 14 at 0:18

























                    answered Jan 13 at 23:53









                    Foobaz JohnFoobaz John

                    23k41552




                    23k41552























                        3












                        $begingroup$

                        Usually you're supposed to give some context and explain what you've tried so far. However, I will take your word that you have been "slowly losing" your mind and give an answer.



                        Since this is a nonlinear inequality, there is no "cookie cutter" way to solve it. But you can get an idea of what to do by graphing $y_1=2/x$ and $y_2=3x$, and observing where $y_1>y_2$.



                        See here for a graph with $y_1=2/x$ in red and $y_2=3x$ in blue. Where does the red curve lie above the blue curve?



                        Well, you can see that there are two intersection points. But the red lies above the blue from $-infty$ up to the first intersection point, and then again from zero to the second intersection point.



                        To find the intersection points, set $2/x=3x$ and solve.



                        Can you write down the final answer?






                        share|cite|improve this answer









                        $endgroup$


















                          3












                          $begingroup$

                          Usually you're supposed to give some context and explain what you've tried so far. However, I will take your word that you have been "slowly losing" your mind and give an answer.



                          Since this is a nonlinear inequality, there is no "cookie cutter" way to solve it. But you can get an idea of what to do by graphing $y_1=2/x$ and $y_2=3x$, and observing where $y_1>y_2$.



                          See here for a graph with $y_1=2/x$ in red and $y_2=3x$ in blue. Where does the red curve lie above the blue curve?



                          Well, you can see that there are two intersection points. But the red lies above the blue from $-infty$ up to the first intersection point, and then again from zero to the second intersection point.



                          To find the intersection points, set $2/x=3x$ and solve.



                          Can you write down the final answer?






                          share|cite|improve this answer









                          $endgroup$
















                            3












                            3








                            3





                            $begingroup$

                            Usually you're supposed to give some context and explain what you've tried so far. However, I will take your word that you have been "slowly losing" your mind and give an answer.



                            Since this is a nonlinear inequality, there is no "cookie cutter" way to solve it. But you can get an idea of what to do by graphing $y_1=2/x$ and $y_2=3x$, and observing where $y_1>y_2$.



                            See here for a graph with $y_1=2/x$ in red and $y_2=3x$ in blue. Where does the red curve lie above the blue curve?



                            Well, you can see that there are two intersection points. But the red lies above the blue from $-infty$ up to the first intersection point, and then again from zero to the second intersection point.



                            To find the intersection points, set $2/x=3x$ and solve.



                            Can you write down the final answer?






                            share|cite|improve this answer









                            $endgroup$



                            Usually you're supposed to give some context and explain what you've tried so far. However, I will take your word that you have been "slowly losing" your mind and give an answer.



                            Since this is a nonlinear inequality, there is no "cookie cutter" way to solve it. But you can get an idea of what to do by graphing $y_1=2/x$ and $y_2=3x$, and observing where $y_1>y_2$.



                            See here for a graph with $y_1=2/x$ in red and $y_2=3x$ in blue. Where does the red curve lie above the blue curve?



                            Well, you can see that there are two intersection points. But the red lies above the blue from $-infty$ up to the first intersection point, and then again from zero to the second intersection point.



                            To find the intersection points, set $2/x=3x$ and solve.



                            Can you write down the final answer?







                            share|cite|improve this answer












                            share|cite|improve this answer



                            share|cite|improve this answer










                            answered Jan 13 at 23:59









                            Ben WBen W

                            2,734918




                            2,734918















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