What is the Log of a Complex Variable?

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baby_1
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what is log of z=X+JY?

Thanks
 
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We can always write x+ iy in "polar form": [itex]x+ iy= re^{i\theta}[/itex] where [itex]r= \sqrt{x^2+ y^2}[/itex] and [itex]\theta= arctan(y/x)[/itex].

Then [itex]ln(x+ iy)= ln(re^{i\theta})= ln(r)+ i\theta[/itex]. Of course, because tangent is periodic, with period [itex]\pi[/itex], ln is not a single-valued function:
[itex]ln(x+ iy)= ln(r)+ i(\theta+ n\pi)[/itex] for n any integer.