Evaluate $(1+i)^(1-2i)$

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Find all the values of $(1+i)^(1-2i)$ and show that there are small values as we wish (else from $0$) and big values as we wish



beginalign
(1+i)^(1-2i)&=e^ln(1+i)^(1-2i)
=e^(1-2i)ln(1+i)
\&=e^(lnsqrt2+i(fracpi2+2pi k))(1-2i)
\&=e^lnsqrt2-2lnsqrt2*i+i(fracpi2+2pi k)+2(fracpi2+2pi k))
\&=sqrt2*e^-2lnsqrt2*i*i*e^2(fracpi2+2pi k)
\&=e^-2lnsqrt2*i+pi+4pi k+isqrt2
\&=e^-i(2lnsqrt2+i(pi+4pi k))+isqrt2
\&=e^-i*e^(2lnsqrt2+i(pi+4pi k))+isqrt2
\&=frac34*e^(2lnsqrt2+i(pi+4pi k))+isqrt2
\&=frac34*2e^i(pi+4pi k)+isqrt2
\&=frac-32+isqrt2
endalign



What can I conclude from it on the values?



Or should I stop here $e^-2lnsqrt2*i+pi+4pi k+isqrt2$ and $e^pi+4 pi kcis(-2lnsqrt2+fracpi2)$







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  • 1




    This is quite difficult to read. Consider using beginalign and endalign.
    – TheSimpliFire
    Jul 17 at 7:46










  • @TheSimpliFire added
    – gbox
    Jul 17 at 7:52






  • 2




    In line 7 you used the wrong formula $e^-iz=e^-ie^z$.
    – Kavi Rama Murthy
    Jul 17 at 7:59











  • Somehow along the way (line 4->5) one multiplication mutated into an addition. You should not get a sum from your formula.
    – LutzL
    Jul 17 at 8:00















up vote
1
down vote

favorite
1












Find all the values of $(1+i)^(1-2i)$ and show that there are small values as we wish (else from $0$) and big values as we wish



beginalign
(1+i)^(1-2i)&=e^ln(1+i)^(1-2i)
=e^(1-2i)ln(1+i)
\&=e^(lnsqrt2+i(fracpi2+2pi k))(1-2i)
\&=e^lnsqrt2-2lnsqrt2*i+i(fracpi2+2pi k)+2(fracpi2+2pi k))
\&=sqrt2*e^-2lnsqrt2*i*i*e^2(fracpi2+2pi k)
\&=e^-2lnsqrt2*i+pi+4pi k+isqrt2
\&=e^-i(2lnsqrt2+i(pi+4pi k))+isqrt2
\&=e^-i*e^(2lnsqrt2+i(pi+4pi k))+isqrt2
\&=frac34*e^(2lnsqrt2+i(pi+4pi k))+isqrt2
\&=frac34*2e^i(pi+4pi k)+isqrt2
\&=frac-32+isqrt2
endalign



What can I conclude from it on the values?



Or should I stop here $e^-2lnsqrt2*i+pi+4pi k+isqrt2$ and $e^pi+4 pi kcis(-2lnsqrt2+fracpi2)$







share|cite|improve this question

















  • 1




    This is quite difficult to read. Consider using beginalign and endalign.
    – TheSimpliFire
    Jul 17 at 7:46










  • @TheSimpliFire added
    – gbox
    Jul 17 at 7:52






  • 2




    In line 7 you used the wrong formula $e^-iz=e^-ie^z$.
    – Kavi Rama Murthy
    Jul 17 at 7:59











  • Somehow along the way (line 4->5) one multiplication mutated into an addition. You should not get a sum from your formula.
    – LutzL
    Jul 17 at 8:00













up vote
1
down vote

favorite
1









up vote
1
down vote

favorite
1






1





Find all the values of $(1+i)^(1-2i)$ and show that there are small values as we wish (else from $0$) and big values as we wish



beginalign
(1+i)^(1-2i)&=e^ln(1+i)^(1-2i)
=e^(1-2i)ln(1+i)
\&=e^(lnsqrt2+i(fracpi2+2pi k))(1-2i)
\&=e^lnsqrt2-2lnsqrt2*i+i(fracpi2+2pi k)+2(fracpi2+2pi k))
\&=sqrt2*e^-2lnsqrt2*i*i*e^2(fracpi2+2pi k)
\&=e^-2lnsqrt2*i+pi+4pi k+isqrt2
\&=e^-i(2lnsqrt2+i(pi+4pi k))+isqrt2
\&=e^-i*e^(2lnsqrt2+i(pi+4pi k))+isqrt2
\&=frac34*e^(2lnsqrt2+i(pi+4pi k))+isqrt2
\&=frac34*2e^i(pi+4pi k)+isqrt2
\&=frac-32+isqrt2
endalign



What can I conclude from it on the values?



Or should I stop here $e^-2lnsqrt2*i+pi+4pi k+isqrt2$ and $e^pi+4 pi kcis(-2lnsqrt2+fracpi2)$







share|cite|improve this question













Find all the values of $(1+i)^(1-2i)$ and show that there are small values as we wish (else from $0$) and big values as we wish



beginalign
(1+i)^(1-2i)&=e^ln(1+i)^(1-2i)
=e^(1-2i)ln(1+i)
\&=e^(lnsqrt2+i(fracpi2+2pi k))(1-2i)
\&=e^lnsqrt2-2lnsqrt2*i+i(fracpi2+2pi k)+2(fracpi2+2pi k))
\&=sqrt2*e^-2lnsqrt2*i*i*e^2(fracpi2+2pi k)
\&=e^-2lnsqrt2*i+pi+4pi k+isqrt2
\&=e^-i(2lnsqrt2+i(pi+4pi k))+isqrt2
\&=e^-i*e^(2lnsqrt2+i(pi+4pi k))+isqrt2
\&=frac34*e^(2lnsqrt2+i(pi+4pi k))+isqrt2
\&=frac34*2e^i(pi+4pi k)+isqrt2
\&=frac-32+isqrt2
endalign



What can I conclude from it on the values?



Or should I stop here $e^-2lnsqrt2*i+pi+4pi k+isqrt2$ and $e^pi+4 pi kcis(-2lnsqrt2+fracpi2)$









share|cite|improve this question












share|cite|improve this question




share|cite|improve this question








edited Jul 17 at 7:59









LutzL

49.8k31849




49.8k31849









asked Jul 17 at 7:36









gbox

5,30851841




5,30851841







  • 1




    This is quite difficult to read. Consider using beginalign and endalign.
    – TheSimpliFire
    Jul 17 at 7:46










  • @TheSimpliFire added
    – gbox
    Jul 17 at 7:52






  • 2




    In line 7 you used the wrong formula $e^-iz=e^-ie^z$.
    – Kavi Rama Murthy
    Jul 17 at 7:59











  • Somehow along the way (line 4->5) one multiplication mutated into an addition. You should not get a sum from your formula.
    – LutzL
    Jul 17 at 8:00













  • 1




    This is quite difficult to read. Consider using beginalign and endalign.
    – TheSimpliFire
    Jul 17 at 7:46










  • @TheSimpliFire added
    – gbox
    Jul 17 at 7:52






  • 2




    In line 7 you used the wrong formula $e^-iz=e^-ie^z$.
    – Kavi Rama Murthy
    Jul 17 at 7:59











  • Somehow along the way (line 4->5) one multiplication mutated into an addition. You should not get a sum from your formula.
    – LutzL
    Jul 17 at 8:00








1




1




This is quite difficult to read. Consider using beginalign and endalign.
– TheSimpliFire
Jul 17 at 7:46




This is quite difficult to read. Consider using beginalign and endalign.
– TheSimpliFire
Jul 17 at 7:46












@TheSimpliFire added
– gbox
Jul 17 at 7:52




@TheSimpliFire added
– gbox
Jul 17 at 7:52




2




2




In line 7 you used the wrong formula $e^-iz=e^-ie^z$.
– Kavi Rama Murthy
Jul 17 at 7:59





In line 7 you used the wrong formula $e^-iz=e^-ie^z$.
– Kavi Rama Murthy
Jul 17 at 7:59













Somehow along the way (line 4->5) one multiplication mutated into an addition. You should not get a sum from your formula.
– LutzL
Jul 17 at 8:00





Somehow along the way (line 4->5) one multiplication mutated into an addition. You should not get a sum from your formula.
– LutzL
Jul 17 at 8:00











2 Answers
2






active

oldest

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up vote
2
down vote



accepted










Hint. Note that $|e^z|=|e^textRe(z)+itextIm(z)|=e^textRe(z)$, hence here we are interested in (see your third step where the correct argument of $(1+i)$ is $pi/4+2pi k$)
$$textRe(lnsqrt2+i(fracpi4+2pi k))(1-2i))=lnsqrt2+pileft(4k+frac12right)$$
where $kinmathbbZ$. Now consider the limits as $kto pm infty$.






share|cite|improve this answer























  • Should it be $lnsqrt2+pi (4k+frac12)$?
    – gbox
    Jul 17 at 8:15











  • Yes, you are right.
    – Robert Z
    Jul 17 at 8:30

















up vote
0
down vote













There should only be one value.$$(1+i)^1-2i=(sqrt 2e^dfracipi4)^1-2i=sqrt 2e^dfracipi4(0.5e^dfrac-ipi2)^i=sqrt 2e^dfracpi2e^i(dfracpi4+ln 0.5)$$






share|cite|improve this answer





















  • There is not. $ $
    – Did
    Jul 17 at 8:38










  • What you said means that $(dfrac12)^i$ should have different values. Why should it be so?
    – Mostafa Ayaz
    Jul 17 at 8:40










  • You should be the one telling us why -- or why you choose to answer questions on subjects you obviously do not master?
    – Did
    Jul 17 at 8:42










  • Wooow not so fast! If one quantity or expression is multivalued one must say why is that so not the one ascribing only one variable to it, for example nobody asks why $2^2$ has only one value but if somebody claims another value he should explain.
    – Mostafa Ayaz
    Jul 17 at 8:50










  • Yes, "so fast". You may not be realizing it but, posting this, you are squarely ignoring the basics of the domain (call it "complex analysis" if you wish). Again, you should explain why you see fit to post wrong answers.
    – Did
    Jul 17 at 8:55










Your Answer




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2 Answers
2






active

oldest

votes








2 Answers
2






active

oldest

votes









active

oldest

votes






active

oldest

votes








up vote
2
down vote



accepted










Hint. Note that $|e^z|=|e^textRe(z)+itextIm(z)|=e^textRe(z)$, hence here we are interested in (see your third step where the correct argument of $(1+i)$ is $pi/4+2pi k$)
$$textRe(lnsqrt2+i(fracpi4+2pi k))(1-2i))=lnsqrt2+pileft(4k+frac12right)$$
where $kinmathbbZ$. Now consider the limits as $kto pm infty$.






share|cite|improve this answer























  • Should it be $lnsqrt2+pi (4k+frac12)$?
    – gbox
    Jul 17 at 8:15











  • Yes, you are right.
    – Robert Z
    Jul 17 at 8:30














up vote
2
down vote



accepted










Hint. Note that $|e^z|=|e^textRe(z)+itextIm(z)|=e^textRe(z)$, hence here we are interested in (see your third step where the correct argument of $(1+i)$ is $pi/4+2pi k$)
$$textRe(lnsqrt2+i(fracpi4+2pi k))(1-2i))=lnsqrt2+pileft(4k+frac12right)$$
where $kinmathbbZ$. Now consider the limits as $kto pm infty$.






share|cite|improve this answer























  • Should it be $lnsqrt2+pi (4k+frac12)$?
    – gbox
    Jul 17 at 8:15











  • Yes, you are right.
    – Robert Z
    Jul 17 at 8:30












up vote
2
down vote



accepted







up vote
2
down vote



accepted






Hint. Note that $|e^z|=|e^textRe(z)+itextIm(z)|=e^textRe(z)$, hence here we are interested in (see your third step where the correct argument of $(1+i)$ is $pi/4+2pi k$)
$$textRe(lnsqrt2+i(fracpi4+2pi k))(1-2i))=lnsqrt2+pileft(4k+frac12right)$$
where $kinmathbbZ$. Now consider the limits as $kto pm infty$.






share|cite|improve this answer















Hint. Note that $|e^z|=|e^textRe(z)+itextIm(z)|=e^textRe(z)$, hence here we are interested in (see your third step where the correct argument of $(1+i)$ is $pi/4+2pi k$)
$$textRe(lnsqrt2+i(fracpi4+2pi k))(1-2i))=lnsqrt2+pileft(4k+frac12right)$$
where $kinmathbbZ$. Now consider the limits as $kto pm infty$.







share|cite|improve this answer















share|cite|improve this answer



share|cite|improve this answer








edited Jul 17 at 8:30


























answered Jul 17 at 7:59









Robert Z

84.2k955123




84.2k955123











  • Should it be $lnsqrt2+pi (4k+frac12)$?
    – gbox
    Jul 17 at 8:15











  • Yes, you are right.
    – Robert Z
    Jul 17 at 8:30
















  • Should it be $lnsqrt2+pi (4k+frac12)$?
    – gbox
    Jul 17 at 8:15











  • Yes, you are right.
    – Robert Z
    Jul 17 at 8:30















Should it be $lnsqrt2+pi (4k+frac12)$?
– gbox
Jul 17 at 8:15





Should it be $lnsqrt2+pi (4k+frac12)$?
– gbox
Jul 17 at 8:15













Yes, you are right.
– Robert Z
Jul 17 at 8:30




Yes, you are right.
– Robert Z
Jul 17 at 8:30










up vote
0
down vote













There should only be one value.$$(1+i)^1-2i=(sqrt 2e^dfracipi4)^1-2i=sqrt 2e^dfracipi4(0.5e^dfrac-ipi2)^i=sqrt 2e^dfracpi2e^i(dfracpi4+ln 0.5)$$






share|cite|improve this answer





















  • There is not. $ $
    – Did
    Jul 17 at 8:38










  • What you said means that $(dfrac12)^i$ should have different values. Why should it be so?
    – Mostafa Ayaz
    Jul 17 at 8:40










  • You should be the one telling us why -- or why you choose to answer questions on subjects you obviously do not master?
    – Did
    Jul 17 at 8:42










  • Wooow not so fast! If one quantity or expression is multivalued one must say why is that so not the one ascribing only one variable to it, for example nobody asks why $2^2$ has only one value but if somebody claims another value he should explain.
    – Mostafa Ayaz
    Jul 17 at 8:50










  • Yes, "so fast". You may not be realizing it but, posting this, you are squarely ignoring the basics of the domain (call it "complex analysis" if you wish). Again, you should explain why you see fit to post wrong answers.
    – Did
    Jul 17 at 8:55














up vote
0
down vote













There should only be one value.$$(1+i)^1-2i=(sqrt 2e^dfracipi4)^1-2i=sqrt 2e^dfracipi4(0.5e^dfrac-ipi2)^i=sqrt 2e^dfracpi2e^i(dfracpi4+ln 0.5)$$






share|cite|improve this answer





















  • There is not. $ $
    – Did
    Jul 17 at 8:38










  • What you said means that $(dfrac12)^i$ should have different values. Why should it be so?
    – Mostafa Ayaz
    Jul 17 at 8:40










  • You should be the one telling us why -- or why you choose to answer questions on subjects you obviously do not master?
    – Did
    Jul 17 at 8:42










  • Wooow not so fast! If one quantity or expression is multivalued one must say why is that so not the one ascribing only one variable to it, for example nobody asks why $2^2$ has only one value but if somebody claims another value he should explain.
    – Mostafa Ayaz
    Jul 17 at 8:50










  • Yes, "so fast". You may not be realizing it but, posting this, you are squarely ignoring the basics of the domain (call it "complex analysis" if you wish). Again, you should explain why you see fit to post wrong answers.
    – Did
    Jul 17 at 8:55












up vote
0
down vote










up vote
0
down vote









There should only be one value.$$(1+i)^1-2i=(sqrt 2e^dfracipi4)^1-2i=sqrt 2e^dfracipi4(0.5e^dfrac-ipi2)^i=sqrt 2e^dfracpi2e^i(dfracpi4+ln 0.5)$$






share|cite|improve this answer













There should only be one value.$$(1+i)^1-2i=(sqrt 2e^dfracipi4)^1-2i=sqrt 2e^dfracipi4(0.5e^dfrac-ipi2)^i=sqrt 2e^dfracpi2e^i(dfracpi4+ln 0.5)$$







share|cite|improve this answer













share|cite|improve this answer



share|cite|improve this answer











answered Jul 17 at 8:04









Mostafa Ayaz

8,6023630




8,6023630











  • There is not. $ $
    – Did
    Jul 17 at 8:38










  • What you said means that $(dfrac12)^i$ should have different values. Why should it be so?
    – Mostafa Ayaz
    Jul 17 at 8:40










  • You should be the one telling us why -- or why you choose to answer questions on subjects you obviously do not master?
    – Did
    Jul 17 at 8:42










  • Wooow not so fast! If one quantity or expression is multivalued one must say why is that so not the one ascribing only one variable to it, for example nobody asks why $2^2$ has only one value but if somebody claims another value he should explain.
    – Mostafa Ayaz
    Jul 17 at 8:50










  • Yes, "so fast". You may not be realizing it but, posting this, you are squarely ignoring the basics of the domain (call it "complex analysis" if you wish). Again, you should explain why you see fit to post wrong answers.
    – Did
    Jul 17 at 8:55
















  • There is not. $ $
    – Did
    Jul 17 at 8:38










  • What you said means that $(dfrac12)^i$ should have different values. Why should it be so?
    – Mostafa Ayaz
    Jul 17 at 8:40










  • You should be the one telling us why -- or why you choose to answer questions on subjects you obviously do not master?
    – Did
    Jul 17 at 8:42










  • Wooow not so fast! If one quantity or expression is multivalued one must say why is that so not the one ascribing only one variable to it, for example nobody asks why $2^2$ has only one value but if somebody claims another value he should explain.
    – Mostafa Ayaz
    Jul 17 at 8:50










  • Yes, "so fast". You may not be realizing it but, posting this, you are squarely ignoring the basics of the domain (call it "complex analysis" if you wish). Again, you should explain why you see fit to post wrong answers.
    – Did
    Jul 17 at 8:55















There is not. $ $
– Did
Jul 17 at 8:38




There is not. $ $
– Did
Jul 17 at 8:38












What you said means that $(dfrac12)^i$ should have different values. Why should it be so?
– Mostafa Ayaz
Jul 17 at 8:40




What you said means that $(dfrac12)^i$ should have different values. Why should it be so?
– Mostafa Ayaz
Jul 17 at 8:40












You should be the one telling us why -- or why you choose to answer questions on subjects you obviously do not master?
– Did
Jul 17 at 8:42




You should be the one telling us why -- or why you choose to answer questions on subjects you obviously do not master?
– Did
Jul 17 at 8:42












Wooow not so fast! If one quantity or expression is multivalued one must say why is that so not the one ascribing only one variable to it, for example nobody asks why $2^2$ has only one value but if somebody claims another value he should explain.
– Mostafa Ayaz
Jul 17 at 8:50




Wooow not so fast! If one quantity or expression is multivalued one must say why is that so not the one ascribing only one variable to it, for example nobody asks why $2^2$ has only one value but if somebody claims another value he should explain.
– Mostafa Ayaz
Jul 17 at 8:50












Yes, "so fast". You may not be realizing it but, posting this, you are squarely ignoring the basics of the domain (call it "complex analysis" if you wish). Again, you should explain why you see fit to post wrong answers.
– Did
Jul 17 at 8:55




Yes, "so fast". You may not be realizing it but, posting this, you are squarely ignoring the basics of the domain (call it "complex analysis" if you wish). Again, you should explain why you see fit to post wrong answers.
– Did
Jul 17 at 8:55












 

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