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Value of an expression involving complex numbers

Uniman

New member
Oct 19, 2012
11
php0Lf6W7.png

The answer is a number....

Work done so far

3^3 * 3^( i8pi/ln(3) ) = 27 * (3^ i8pi - 3^ln(3) ) = 27 *( 3^25.1i -3.34)


= 3^(3+ i25.1) - 90.26

If this is correct how can I convert this to a number.....
 

chisigma

Well-known member
Feb 13, 2012
1,704
Re: Complex function

View attachment 423

The answer is a number....

Work done so far

3^3 * 3^( i8pi/ln(3) ) = 27 * (3^ i8pi - 3^ln(3) ) = 27 *( 3^25.1i -3.34)


= 3^(3+ i25.1) - 90.26

If this is correct how can I convert this to a number.....
You can use Euler's identity to 'discover' that is...

$\displaystyle 3^{3 + i\ \frac{8\ \pi}{\ln 3}}= e^{3\ \ln 3}= 27$

Kind regards

$\chi$ $\sigma$
 
Last edited by a moderator:

soroban

Well-known member
Feb 2, 2012
409
Re: Complex function

Hello, Uniman!

[tex]\text{Evaluate: }\:X \;=\;3^{3 + \frac{8\pi}{\ln(3)}i}[/tex]

We have: .[tex]X \;=\;3^3\cdot3^{\frac{8\pi}{\ln(3)}i} \;=\;27\cdot 3^{\frac{8\pi}{\ln(3)}i} [/tex] .[1]

[tex]\text{Let }y \:=\:3^{\frac{8\pi}{\ln(3)}i} [/tex]

[tex]\text{Take logs: }\:\ln(y) \;=\;\ln\left(3^{\frac{8\pi}{\ln(3)}i}\right) \;=\;\frac{8\pi}{\ln(3)}i\cdot\ln(3) \;=\;8\pi i[/tex]

. . [tex]y \;=\;e^{8\pi i} \;=\;\left(e^{i\pi}\right)^8 \;=\;(\text{-}1)^8 \;=\;1[/tex]


Substitute into [1]: .[tex]X \;=\;27\cdot1 \;=\;\boxed{27}[/tex]