How to find all the $z$ that satisfy $(1+i)z^4=(1-i)|z|^2$?

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Would you please help me solve this? I need all the $z$ that satisfy the equality



$$(1+i)z^4=(1-i)|z|^2.$$



I tried doing this:



$$
beginaligned
(1+i)z^4&= (1-i)zoverline z\
(1+i)z^4 -(1-i)zoverline z &= 0\
z[(1+i)z^3-(1-i)overline z]&= 0
endaligned
$$



Then $z= 0$ and
$$(1+i)z^3-(1-i)overline z= 0.$$



I don't know what to do with $overline z$.










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  • 2




    Consider the absolute value of both sides, then you can easily see that $z$ must be uni-modular or zero. That is $|z|=0, 1.$ Than take $z=costheta+isintheta$ and substitute to your equation to find particular conditions on $theta.$
    – Bumblebee
    Aug 20 at 0:57















up vote
3
down vote

favorite












Would you please help me solve this? I need all the $z$ that satisfy the equality



$$(1+i)z^4=(1-i)|z|^2.$$



I tried doing this:



$$
beginaligned
(1+i)z^4&= (1-i)zoverline z\
(1+i)z^4 -(1-i)zoverline z &= 0\
z[(1+i)z^3-(1-i)overline z]&= 0
endaligned
$$



Then $z= 0$ and
$$(1+i)z^3-(1-i)overline z= 0.$$



I don't know what to do with $overline z$.










share|cite|improve this question



















  • 2




    Consider the absolute value of both sides, then you can easily see that $z$ must be uni-modular or zero. That is $|z|=0, 1.$ Than take $z=costheta+isintheta$ and substitute to your equation to find particular conditions on $theta.$
    – Bumblebee
    Aug 20 at 0:57













up vote
3
down vote

favorite









up vote
3
down vote

favorite











Would you please help me solve this? I need all the $z$ that satisfy the equality



$$(1+i)z^4=(1-i)|z|^2.$$



I tried doing this:



$$
beginaligned
(1+i)z^4&= (1-i)zoverline z\
(1+i)z^4 -(1-i)zoverline z &= 0\
z[(1+i)z^3-(1-i)overline z]&= 0
endaligned
$$



Then $z= 0$ and
$$(1+i)z^3-(1-i)overline z= 0.$$



I don't know what to do with $overline z$.










share|cite|improve this question















Would you please help me solve this? I need all the $z$ that satisfy the equality



$$(1+i)z^4=(1-i)|z|^2.$$



I tried doing this:



$$
beginaligned
(1+i)z^4&= (1-i)zoverline z\
(1+i)z^4 -(1-i)zoverline z &= 0\
z[(1+i)z^3-(1-i)overline z]&= 0
endaligned
$$



Then $z= 0$ and
$$(1+i)z^3-(1-i)overline z= 0.$$



I don't know what to do with $overline z$.







calculus complex-analysis complex-numbers






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edited Aug 20 at 3:26









AccidentalFourierTransform

1,335627




1,335627










asked Aug 19 at 23:06









tina_98

636




636







  • 2




    Consider the absolute value of both sides, then you can easily see that $z$ must be uni-modular or zero. That is $|z|=0, 1.$ Than take $z=costheta+isintheta$ and substitute to your equation to find particular conditions on $theta.$
    – Bumblebee
    Aug 20 at 0:57













  • 2




    Consider the absolute value of both sides, then you can easily see that $z$ must be uni-modular or zero. That is $|z|=0, 1.$ Than take $z=costheta+isintheta$ and substitute to your equation to find particular conditions on $theta.$
    – Bumblebee
    Aug 20 at 0:57








2




2




Consider the absolute value of both sides, then you can easily see that $z$ must be uni-modular or zero. That is $|z|=0, 1.$ Than take $z=costheta+isintheta$ and substitute to your equation to find particular conditions on $theta.$
– Bumblebee
Aug 20 at 0:57





Consider the absolute value of both sides, then you can easily see that $z$ must be uni-modular or zero. That is $|z|=0, 1.$ Than take $z=costheta+isintheta$ and substitute to your equation to find particular conditions on $theta.$
– Bumblebee
Aug 20 at 0:57











2 Answers
2






active

oldest

votes

















up vote
6
down vote













Hint



$$(1+i)z^4=(1-i)|z|^2iff z^4=dfrac1-i1+i|z|^2=-i|z|^2.$$



Taking modulus we have $|z|=0$ or $|z|=1.$ In the first case it is $z=0.$ In the second case $z=e^itheta.$ So, we have



$$cos (4theta)+isin(4theta)=-i.$$ That is, we have to solve



begincasescos(4theta)=0\sin(4theta)=-1endcases






share|cite|improve this answer






















  • I dont understand why you consider the modulus as 0 and 1
    – tina_98
    Aug 19 at 23:34










  • $z^4=-i|z|^2implies |z|^4=|z^4|=|-i|z|^2|=|-i||z|^2=|z|^2implies |z|^4=|z|^2.$
    – mfl
    Aug 19 at 23:35







  • 1




    There is an easier way to solve $e^4itheta=-i$. Just use $e^4itheta=e^3pi i/2+2kpi i$, or $4itheta=3pi/2 i+2kpi i$.
    – Rory Daulton
    Aug 20 at 0:16


















up vote
0
down vote













$$(1+i)z^4=(1-i)|z|^2iff iz^4=zbar ziffbegincasesz=0\iz^3=bar zendcases$$ $$iz^3=bar ziff i(a+ib)^3=(a-ib)iff ia^3 - 3 a^2 b -i 3 a b^2 + b^3=(a-ib)\iff b^3- 3 a^2 b +i(a^3 - 3 a b^2)=a-ibiffbegincasesb^3- 3 a^2 b=a\a^3 - 3 a b^2=-bendcases$$



We can also notice that $|b^3- 3 a^2 b +i(a^3 - 3 a b^2)|=sqrt(a^2+b^2)^3=sqrta^2+b^2=|a-ib|implies
|z|=begincases1\0endcases$, so it comes with terms with @mfl's answer






share|cite|improve this answer
















  • 1




    No idea why you send the OP to the real part / imaginary part decomposition when it only complicates things. How would you solve $iz^9=bar z$, one wonders...
    – Did
    Aug 20 at 18:41











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2 Answers
2






active

oldest

votes








2 Answers
2






active

oldest

votes









active

oldest

votes






active

oldest

votes








up vote
6
down vote













Hint



$$(1+i)z^4=(1-i)|z|^2iff z^4=dfrac1-i1+i|z|^2=-i|z|^2.$$



Taking modulus we have $|z|=0$ or $|z|=1.$ In the first case it is $z=0.$ In the second case $z=e^itheta.$ So, we have



$$cos (4theta)+isin(4theta)=-i.$$ That is, we have to solve



begincasescos(4theta)=0\sin(4theta)=-1endcases






share|cite|improve this answer






















  • I dont understand why you consider the modulus as 0 and 1
    – tina_98
    Aug 19 at 23:34










  • $z^4=-i|z|^2implies |z|^4=|z^4|=|-i|z|^2|=|-i||z|^2=|z|^2implies |z|^4=|z|^2.$
    – mfl
    Aug 19 at 23:35







  • 1




    There is an easier way to solve $e^4itheta=-i$. Just use $e^4itheta=e^3pi i/2+2kpi i$, or $4itheta=3pi/2 i+2kpi i$.
    – Rory Daulton
    Aug 20 at 0:16















up vote
6
down vote













Hint



$$(1+i)z^4=(1-i)|z|^2iff z^4=dfrac1-i1+i|z|^2=-i|z|^2.$$



Taking modulus we have $|z|=0$ or $|z|=1.$ In the first case it is $z=0.$ In the second case $z=e^itheta.$ So, we have



$$cos (4theta)+isin(4theta)=-i.$$ That is, we have to solve



begincasescos(4theta)=0\sin(4theta)=-1endcases






share|cite|improve this answer






















  • I dont understand why you consider the modulus as 0 and 1
    – tina_98
    Aug 19 at 23:34










  • $z^4=-i|z|^2implies |z|^4=|z^4|=|-i|z|^2|=|-i||z|^2=|z|^2implies |z|^4=|z|^2.$
    – mfl
    Aug 19 at 23:35







  • 1




    There is an easier way to solve $e^4itheta=-i$. Just use $e^4itheta=e^3pi i/2+2kpi i$, or $4itheta=3pi/2 i+2kpi i$.
    – Rory Daulton
    Aug 20 at 0:16













up vote
6
down vote










up vote
6
down vote









Hint



$$(1+i)z^4=(1-i)|z|^2iff z^4=dfrac1-i1+i|z|^2=-i|z|^2.$$



Taking modulus we have $|z|=0$ or $|z|=1.$ In the first case it is $z=0.$ In the second case $z=e^itheta.$ So, we have



$$cos (4theta)+isin(4theta)=-i.$$ That is, we have to solve



begincasescos(4theta)=0\sin(4theta)=-1endcases






share|cite|improve this answer














Hint



$$(1+i)z^4=(1-i)|z|^2iff z^4=dfrac1-i1+i|z|^2=-i|z|^2.$$



Taking modulus we have $|z|=0$ or $|z|=1.$ In the first case it is $z=0.$ In the second case $z=e^itheta.$ So, we have



$$cos (4theta)+isin(4theta)=-i.$$ That is, we have to solve



begincasescos(4theta)=0\sin(4theta)=-1endcases







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited Aug 19 at 23:32

























answered Aug 19 at 23:16









mfl

25.2k12141




25.2k12141











  • I dont understand why you consider the modulus as 0 and 1
    – tina_98
    Aug 19 at 23:34










  • $z^4=-i|z|^2implies |z|^4=|z^4|=|-i|z|^2|=|-i||z|^2=|z|^2implies |z|^4=|z|^2.$
    – mfl
    Aug 19 at 23:35







  • 1




    There is an easier way to solve $e^4itheta=-i$. Just use $e^4itheta=e^3pi i/2+2kpi i$, or $4itheta=3pi/2 i+2kpi i$.
    – Rory Daulton
    Aug 20 at 0:16

















  • I dont understand why you consider the modulus as 0 and 1
    – tina_98
    Aug 19 at 23:34










  • $z^4=-i|z|^2implies |z|^4=|z^4|=|-i|z|^2|=|-i||z|^2=|z|^2implies |z|^4=|z|^2.$
    – mfl
    Aug 19 at 23:35







  • 1




    There is an easier way to solve $e^4itheta=-i$. Just use $e^4itheta=e^3pi i/2+2kpi i$, or $4itheta=3pi/2 i+2kpi i$.
    – Rory Daulton
    Aug 20 at 0:16
















I dont understand why you consider the modulus as 0 and 1
– tina_98
Aug 19 at 23:34




I dont understand why you consider the modulus as 0 and 1
– tina_98
Aug 19 at 23:34












$z^4=-i|z|^2implies |z|^4=|z^4|=|-i|z|^2|=|-i||z|^2=|z|^2implies |z|^4=|z|^2.$
– mfl
Aug 19 at 23:35





$z^4=-i|z|^2implies |z|^4=|z^4|=|-i|z|^2|=|-i||z|^2=|z|^2implies |z|^4=|z|^2.$
– mfl
Aug 19 at 23:35





1




1




There is an easier way to solve $e^4itheta=-i$. Just use $e^4itheta=e^3pi i/2+2kpi i$, or $4itheta=3pi/2 i+2kpi i$.
– Rory Daulton
Aug 20 at 0:16





There is an easier way to solve $e^4itheta=-i$. Just use $e^4itheta=e^3pi i/2+2kpi i$, or $4itheta=3pi/2 i+2kpi i$.
– Rory Daulton
Aug 20 at 0:16











up vote
0
down vote













$$(1+i)z^4=(1-i)|z|^2iff iz^4=zbar ziffbegincasesz=0\iz^3=bar zendcases$$ $$iz^3=bar ziff i(a+ib)^3=(a-ib)iff ia^3 - 3 a^2 b -i 3 a b^2 + b^3=(a-ib)\iff b^3- 3 a^2 b +i(a^3 - 3 a b^2)=a-ibiffbegincasesb^3- 3 a^2 b=a\a^3 - 3 a b^2=-bendcases$$



We can also notice that $|b^3- 3 a^2 b +i(a^3 - 3 a b^2)|=sqrt(a^2+b^2)^3=sqrta^2+b^2=|a-ib|implies
|z|=begincases1\0endcases$, so it comes with terms with @mfl's answer






share|cite|improve this answer
















  • 1




    No idea why you send the OP to the real part / imaginary part decomposition when it only complicates things. How would you solve $iz^9=bar z$, one wonders...
    – Did
    Aug 20 at 18:41















up vote
0
down vote













$$(1+i)z^4=(1-i)|z|^2iff iz^4=zbar ziffbegincasesz=0\iz^3=bar zendcases$$ $$iz^3=bar ziff i(a+ib)^3=(a-ib)iff ia^3 - 3 a^2 b -i 3 a b^2 + b^3=(a-ib)\iff b^3- 3 a^2 b +i(a^3 - 3 a b^2)=a-ibiffbegincasesb^3- 3 a^2 b=a\a^3 - 3 a b^2=-bendcases$$



We can also notice that $|b^3- 3 a^2 b +i(a^3 - 3 a b^2)|=sqrt(a^2+b^2)^3=sqrta^2+b^2=|a-ib|implies
|z|=begincases1\0endcases$, so it comes with terms with @mfl's answer






share|cite|improve this answer
















  • 1




    No idea why you send the OP to the real part / imaginary part decomposition when it only complicates things. How would you solve $iz^9=bar z$, one wonders...
    – Did
    Aug 20 at 18:41













up vote
0
down vote










up vote
0
down vote









$$(1+i)z^4=(1-i)|z|^2iff iz^4=zbar ziffbegincasesz=0\iz^3=bar zendcases$$ $$iz^3=bar ziff i(a+ib)^3=(a-ib)iff ia^3 - 3 a^2 b -i 3 a b^2 + b^3=(a-ib)\iff b^3- 3 a^2 b +i(a^3 - 3 a b^2)=a-ibiffbegincasesb^3- 3 a^2 b=a\a^3 - 3 a b^2=-bendcases$$



We can also notice that $|b^3- 3 a^2 b +i(a^3 - 3 a b^2)|=sqrt(a^2+b^2)^3=sqrta^2+b^2=|a-ib|implies
|z|=begincases1\0endcases$, so it comes with terms with @mfl's answer






share|cite|improve this answer












$$(1+i)z^4=(1-i)|z|^2iff iz^4=zbar ziffbegincasesz=0\iz^3=bar zendcases$$ $$iz^3=bar ziff i(a+ib)^3=(a-ib)iff ia^3 - 3 a^2 b -i 3 a b^2 + b^3=(a-ib)\iff b^3- 3 a^2 b +i(a^3 - 3 a b^2)=a-ibiffbegincasesb^3- 3 a^2 b=a\a^3 - 3 a b^2=-bendcases$$



We can also notice that $|b^3- 3 a^2 b +i(a^3 - 3 a b^2)|=sqrt(a^2+b^2)^3=sqrta^2+b^2=|a-ib|implies
|z|=begincases1\0endcases$, so it comes with terms with @mfl's answer







share|cite|improve this answer












share|cite|improve this answer



share|cite|improve this answer










answered Aug 20 at 0:17









Holo

4,7472729




4,7472729







  • 1




    No idea why you send the OP to the real part / imaginary part decomposition when it only complicates things. How would you solve $iz^9=bar z$, one wonders...
    – Did
    Aug 20 at 18:41













  • 1




    No idea why you send the OP to the real part / imaginary part decomposition when it only complicates things. How would you solve $iz^9=bar z$, one wonders...
    – Did
    Aug 20 at 18:41








1




1




No idea why you send the OP to the real part / imaginary part decomposition when it only complicates things. How would you solve $iz^9=bar z$, one wonders...
– Did
Aug 20 at 18:41





No idea why you send the OP to the real part / imaginary part decomposition when it only complicates things. How would you solve $iz^9=bar z$, one wonders...
– Did
Aug 20 at 18:41


















 

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