Linking complex loci to vectors












-1












$begingroup$


Find the locus of $z$ such that
$$argleft( frac{ z^2 - 1}{ z^2 + 1} right) = 0~, qquad z neq pm i$$
I am able to solve this by substituting $z$ as $x+iy$ and proceeding algebraically.



My question is




How can I solve for this loci in terms of vectors (maybe with a bit plane geometry)?




For example, if I see an expression of the form |$z$|=$r$, I know that it's a circle.










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  • $begingroup$
    Let's see if my edit is deemed an improvement that can prevent further downvoting and vote-to-close. Sameer Thakur please feel free to overwrite my edit.
    $endgroup$
    – Lee David Chung Lin
    Jan 10 at 12:59
















-1












$begingroup$


Find the locus of $z$ such that
$$argleft( frac{ z^2 - 1}{ z^2 + 1} right) = 0~, qquad z neq pm i$$
I am able to solve this by substituting $z$ as $x+iy$ and proceeding algebraically.



My question is




How can I solve for this loci in terms of vectors (maybe with a bit plane geometry)?




For example, if I see an expression of the form |$z$|=$r$, I know that it's a circle.










share|cite|improve this question











$endgroup$












  • $begingroup$
    Let's see if my edit is deemed an improvement that can prevent further downvoting and vote-to-close. Sameer Thakur please feel free to overwrite my edit.
    $endgroup$
    – Lee David Chung Lin
    Jan 10 at 12:59














-1












-1








-1


0



$begingroup$


Find the locus of $z$ such that
$$argleft( frac{ z^2 - 1}{ z^2 + 1} right) = 0~, qquad z neq pm i$$
I am able to solve this by substituting $z$ as $x+iy$ and proceeding algebraically.



My question is




How can I solve for this loci in terms of vectors (maybe with a bit plane geometry)?




For example, if I see an expression of the form |$z$|=$r$, I know that it's a circle.










share|cite|improve this question











$endgroup$




Find the locus of $z$ such that
$$argleft( frac{ z^2 - 1}{ z^2 + 1} right) = 0~, qquad z neq pm i$$
I am able to solve this by substituting $z$ as $x+iy$ and proceeding algebraically.



My question is




How can I solve for this loci in terms of vectors (maybe with a bit plane geometry)?




For example, if I see an expression of the form |$z$|=$r$, I know that it's a circle.







complex-numbers vectors locus






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share|cite|improve this question













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share|cite|improve this question








edited Jan 10 at 13:00









Lee David Chung Lin

3,88531140




3,88531140










asked Jan 4 at 18:10









Sameer ThakurSameer Thakur

285




285












  • $begingroup$
    Let's see if my edit is deemed an improvement that can prevent further downvoting and vote-to-close. Sameer Thakur please feel free to overwrite my edit.
    $endgroup$
    – Lee David Chung Lin
    Jan 10 at 12:59


















  • $begingroup$
    Let's see if my edit is deemed an improvement that can prevent further downvoting and vote-to-close. Sameer Thakur please feel free to overwrite my edit.
    $endgroup$
    – Lee David Chung Lin
    Jan 10 at 12:59
















$begingroup$
Let's see if my edit is deemed an improvement that can prevent further downvoting and vote-to-close. Sameer Thakur please feel free to overwrite my edit.
$endgroup$
– Lee David Chung Lin
Jan 10 at 12:59




$begingroup$
Let's see if my edit is deemed an improvement that can prevent further downvoting and vote-to-close. Sameer Thakur please feel free to overwrite my edit.
$endgroup$
– Lee David Chung Lin
Jan 10 at 12:59










1 Answer
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$begingroup$

$argleft( frac{ z - z_A}{ z - z_B} right)$ expresses the oriented angle between the vectors $vec{AM}, vec{BM},$ where the points $A,B,M$ represent the complex numbers $z_A, z_B, z$ respectively.



In particular, $argleft( frac{ z - z_A}{ z - z_B} right)=0$ says that the points $A,B$ lie on the same half-line with the bound $M.$ Moreover, $Mneq A$ because $arg$ is not defined for $0,$ and $Mneq B$ for a trivial reason.



Return to the given equation.

The points $Q(z^2)$ such that $0=argleft( frac{ z^2 - 1}{ z^2 + 1} right) = argleft( frac{ z^2 - 1}{ z^2 - (-1)} right)$ are collinear with the points representing $1$ or $-1,$ where $Q$ is the limit point of a convenient half-line. This gives $z^2in (-infty,-1)cup (1,infty).$

From this one concludes easily for $z:$

The locus is the union of four half-lines which are parts of $x-$axis or $y-$axis, and do not contain the segments $[-1,1]$ nor $[-i,i].$






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    $begingroup$

    $argleft( frac{ z - z_A}{ z - z_B} right)$ expresses the oriented angle between the vectors $vec{AM}, vec{BM},$ where the points $A,B,M$ represent the complex numbers $z_A, z_B, z$ respectively.



    In particular, $argleft( frac{ z - z_A}{ z - z_B} right)=0$ says that the points $A,B$ lie on the same half-line with the bound $M.$ Moreover, $Mneq A$ because $arg$ is not defined for $0,$ and $Mneq B$ for a trivial reason.



    Return to the given equation.

    The points $Q(z^2)$ such that $0=argleft( frac{ z^2 - 1}{ z^2 + 1} right) = argleft( frac{ z^2 - 1}{ z^2 - (-1)} right)$ are collinear with the points representing $1$ or $-1,$ where $Q$ is the limit point of a convenient half-line. This gives $z^2in (-infty,-1)cup (1,infty).$

    From this one concludes easily for $z:$

    The locus is the union of four half-lines which are parts of $x-$axis or $y-$axis, and do not contain the segments $[-1,1]$ nor $[-i,i].$






    share|cite|improve this answer









    $endgroup$


















      1












      $begingroup$

      $argleft( frac{ z - z_A}{ z - z_B} right)$ expresses the oriented angle between the vectors $vec{AM}, vec{BM},$ where the points $A,B,M$ represent the complex numbers $z_A, z_B, z$ respectively.



      In particular, $argleft( frac{ z - z_A}{ z - z_B} right)=0$ says that the points $A,B$ lie on the same half-line with the bound $M.$ Moreover, $Mneq A$ because $arg$ is not defined for $0,$ and $Mneq B$ for a trivial reason.



      Return to the given equation.

      The points $Q(z^2)$ such that $0=argleft( frac{ z^2 - 1}{ z^2 + 1} right) = argleft( frac{ z^2 - 1}{ z^2 - (-1)} right)$ are collinear with the points representing $1$ or $-1,$ where $Q$ is the limit point of a convenient half-line. This gives $z^2in (-infty,-1)cup (1,infty).$

      From this one concludes easily for $z:$

      The locus is the union of four half-lines which are parts of $x-$axis or $y-$axis, and do not contain the segments $[-1,1]$ nor $[-i,i].$






      share|cite|improve this answer









      $endgroup$
















        1












        1








        1





        $begingroup$

        $argleft( frac{ z - z_A}{ z - z_B} right)$ expresses the oriented angle between the vectors $vec{AM}, vec{BM},$ where the points $A,B,M$ represent the complex numbers $z_A, z_B, z$ respectively.



        In particular, $argleft( frac{ z - z_A}{ z - z_B} right)=0$ says that the points $A,B$ lie on the same half-line with the bound $M.$ Moreover, $Mneq A$ because $arg$ is not defined for $0,$ and $Mneq B$ for a trivial reason.



        Return to the given equation.

        The points $Q(z^2)$ such that $0=argleft( frac{ z^2 - 1}{ z^2 + 1} right) = argleft( frac{ z^2 - 1}{ z^2 - (-1)} right)$ are collinear with the points representing $1$ or $-1,$ where $Q$ is the limit point of a convenient half-line. This gives $z^2in (-infty,-1)cup (1,infty).$

        From this one concludes easily for $z:$

        The locus is the union of four half-lines which are parts of $x-$axis or $y-$axis, and do not contain the segments $[-1,1]$ nor $[-i,i].$






        share|cite|improve this answer









        $endgroup$



        $argleft( frac{ z - z_A}{ z - z_B} right)$ expresses the oriented angle between the vectors $vec{AM}, vec{BM},$ where the points $A,B,M$ represent the complex numbers $z_A, z_B, z$ respectively.



        In particular, $argleft( frac{ z - z_A}{ z - z_B} right)=0$ says that the points $A,B$ lie on the same half-line with the bound $M.$ Moreover, $Mneq A$ because $arg$ is not defined for $0,$ and $Mneq B$ for a trivial reason.



        Return to the given equation.

        The points $Q(z^2)$ such that $0=argleft( frac{ z^2 - 1}{ z^2 + 1} right) = argleft( frac{ z^2 - 1}{ z^2 - (-1)} right)$ are collinear with the points representing $1$ or $-1,$ where $Q$ is the limit point of a convenient half-line. This gives $z^2in (-infty,-1)cup (1,infty).$

        From this one concludes easily for $z:$

        The locus is the union of four half-lines which are parts of $x-$axis or $y-$axis, and do not contain the segments $[-1,1]$ nor $[-i,i].$







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 10 at 13:50









        user376343user376343

        3,3833826




        3,3833826






























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