Evaluate $(1+i)^(1-2i)$
Clash Royale CLAN TAG#URR8PPP
up vote
1
down vote
favorite
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 $e^pi+4 pi kcis(-2lnsqrt2+fracpi2)$
complex-analysis
add a comment |Â
up vote
1
down vote
favorite
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 $e^pi+4 pi kcis(-2lnsqrt2+fracpi2)$
complex-analysis
1
This is quite difficult to read. Consider usingbeginalign
andendalign
.
– 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
add a comment |Â
up vote
1
down vote
favorite
up vote
1
down vote
favorite
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 $e^pi+4 pi kcis(-2lnsqrt2+fracpi2)$
complex-analysis
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 $e^pi+4 pi kcis(-2lnsqrt2+fracpi2)$
complex-analysis
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 usingbeginalign
andendalign
.
– 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
add a comment |Â
1
This is quite difficult to read. Consider usingbeginalign
andendalign
.
– 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
add a comment |Â
2 Answers
2
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 $kto pm infty$.
Should it be $lnsqrt2+pi (4k+frac12)$?
– gbox
Jul 17 at 8:15
Yes, you are right.
– Robert Z
Jul 17 at 8:30
add a comment |Â
up vote
0
down vote
There should only be one value.$$(1+i)^1-2i=(sqrt 2e^dfracipi4)^1-2i=sqrt 2e^dfracipi4(0.5e^dfrac-ipi2)^i=sqrt 2e^dfracpi2e^i(dfracpi4+ln 0.5)$$
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
add a comment |Â
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 $kto pm infty$.
Should it be $lnsqrt2+pi (4k+frac12)$?
– gbox
Jul 17 at 8:15
Yes, you are right.
– Robert Z
Jul 17 at 8:30
add a comment |Â
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 $kto pm infty$.
Should it be $lnsqrt2+pi (4k+frac12)$?
– gbox
Jul 17 at 8:15
Yes, you are right.
– Robert Z
Jul 17 at 8:30
add a comment |Â
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 $kto pm infty$.
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 $kto pm infty$.
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
add a comment |Â
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
add a comment |Â
up vote
0
down vote
There should only be one value.$$(1+i)^1-2i=(sqrt 2e^dfracipi4)^1-2i=sqrt 2e^dfracipi4(0.5e^dfrac-ipi2)^i=sqrt 2e^dfracpi2e^i(dfracpi4+ln 0.5)$$
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
add a comment |Â
up vote
0
down vote
There should only be one value.$$(1+i)^1-2i=(sqrt 2e^dfracipi4)^1-2i=sqrt 2e^dfracipi4(0.5e^dfrac-ipi2)^i=sqrt 2e^dfracpi2e^i(dfracpi4+ln 0.5)$$
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
add a comment |Â
up vote
0
down vote
up vote
0
down vote
There should only be one value.$$(1+i)^1-2i=(sqrt 2e^dfracipi4)^1-2i=sqrt 2e^dfracipi4(0.5e^dfrac-ipi2)^i=sqrt 2e^dfracpi2e^i(dfracpi4+ln 0.5)$$
There should only be one value.$$(1+i)^1-2i=(sqrt 2e^dfracipi4)^1-2i=sqrt 2e^dfracipi4(0.5e^dfrac-ipi2)^i=sqrt 2e^dfracpi2e^i(dfracpi4+ln 0.5)$$
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
add a comment |Â
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
add a comment |Â
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f2854264%2fevaluate-1i1-2i%23new-answer', 'question_page');
);
Post as a guest
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
1
This is quite difficult to read. Consider using
beginalign
andendalign
.– 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