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[SOLVED] Evaluating imaginary expression

shen07

Member
Aug 14, 2013
54
Find all possible Values of:

2(-i)
 

topsquark

Well-known member
MHB Math Helper
Aug 30, 2012
1,123

shen07

Member
Aug 14, 2013
54
Re: Exercise

well i have tried using

uv=evln(u)

and get cos(ln(2))-isin(ln(2))

but is it the solution because i am asked to find all the possible values
 

ZaidAlyafey

Well-known member
MHB Math Helper
Jan 17, 2013
1,667
Re: Exercise

well i have tried using

uv=evln(u)

and get cos(ln(2))-isin(ln(2))

but is it the solution because i am asked to find all the possible values
The logarithm is a multivalued function so

\(\displaystyle \log(a) = \ln|a|+iarg(a) \)
 

shen07

Member
Aug 14, 2013
54
Re: Exercise

Yes i know that but here we have ln(2) and we cant write this in the above form.
 

ZaidAlyafey

Well-known member
MHB Math Helper
Jan 17, 2013
1,667
Re: Exercise

Yes i know that but here we have ln(2) and we cant write this in the above form.
\(\displaystyle 2^{-i}=e^{-i\log(2)}=e^{-i(\ln|2|+2k\pi i)}\)
 

shen07

Member
Aug 14, 2013
54
Re: Exercise

\(\displaystyle 2^{-i}=e^{-i\log(2)}=e^{-i(\ln|2|+2k\pi i)}\)
but should we not apply complex logarithm ,i.e LOG to complex numbers only, here we should have use LN as far as i have understand. Correct me if i am wrong
 

ZaidAlyafey

Well-known member
MHB Math Helper
Jan 17, 2013
1,667
Re: Exercise

but should we not apply complex logarithm ,i.e LOG to complex numbers only, here we should have use LN as far as i have understand. Correct me if i am wrong
But 2 is still a complex number .

The function

\(\displaystyle e^{\log(2^{-i})}\)

is a multivalued function so it has infinite solutions .
 

shen07

Member
Aug 14, 2013
54
Re: Exercise

But 2 is still a complex number .

The function

\(\displaystyle e^{\log(2^{-i})}\)

is a multivalued function so it has infinite solutions .
ok i understand what you are trying to say. 2 is also found in the complex plane, so we can apply this rule to it, hence obtaining several values with this arbitrary k.

Thanks
 

ZaidAlyafey

Well-known member
MHB Math Helper
Jan 17, 2013
1,667
Re: Exercise

For more information consider the following

\(\displaystyle f(z)=2^{z}\) where $z$ is any complex number .

  1. if $z$ is an integer then the function has only one solution
  2. if $z$ is a rational number then it has finite number of solutions .
  3. If $z$ is any other complex number then it has finitely many solutions .
 

shen07

Member
Aug 14, 2013
54
Re: Exercise

For more information consider the following

\(\displaystyle f(z)=2^{z}\) where $z$ is any complex number .

  1. if $z$ is an integer then the function has only one solution
  2. if $z$ is a rational number then it has finite number of solutions .
  3. If $z$ is any other complex number then it has finitely many solutions .

Thanks a Lot for this Idea..Will remember it..:D