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Principal value of complex number

suvadip

Member
Feb 21, 2013
69
Find all the values of \(\displaystyle (\sqrt{3}+i)^{1/6}\). What is its principle value?I have doubt about the second part. We have heard about the principal value of the amplitude of a complex number. But here the principal value of the complex number itself is asked for. Please help
 

Plato

Well-known member
MHB Math Helper
Jan 27, 2012
196
Re: principal value of complex number

Find all the values of \(\displaystyle (\sqrt{3}+i)^{1/6}\). What is its principle value?
\(\displaystyle \eta = \sqrt[6]{2}\exp \left( {\frac{\pi }{{36}}} \right)\) is one sixth root of \(\displaystyle \sqrt{3}+i\).

If \(\displaystyle \zeta =\exp \left( {\frac{\pi }{{3}}} \right)\) then \(\displaystyle \eta\cdot\zeta^k,~k=0,1,\cdots 5\) are all six.

I have seen \(\displaystyle \eta\) (i.e. \(\displaystyle k=0\)) called the principal root.
 

Prove It

Well-known member
MHB Math Helper
Jan 26, 2012
1,403
Find all the values of \(\displaystyle (\sqrt{3}+i)^{1/6}\). What is its principle value?I have doubt about the second part. We have heard about the principal value of the amplitude of a complex number. But here the principal value of the complex number itself is asked for. Please help
It helps if you remember that there are always two square roots, three cube roots, four fourth roots, etc, and they are all evenly spaced around a circle. So in this case, if you can evaluate one value, the rest will all have the same magnitude and be separated by an angle of \(\displaystyle \displaystyle \frac{2\pi}{6} = \frac{\pi}{3} \).