Problem in Complex Number

[chinmayrshah]

Hello guys,

 

I was working with this complex numbers and got stuck in this confusion. [Pic attached] The confusion is that by solving with two different approaches, the value of [theta] obtained is different.

In the first approach, I obtained argument [theta] = 0. Afterwards, using polar conversion, the argument obtained was [theta] = [pi] for the same problem. Is it possible because else for every complex equation; be it z^4-1, z^6-1, etc...I am getting [theta] = 0.

Am I doing something terribly wrong? Is the complex to polar conversion and vice versa correctly done?

 

Thanks for the help in advance