Solving Complex Number Question z^3+i=0 using z^n=|z|^(n) x e^((i)(n)(theta))

Ry122
Messages
563
Reaction score
2
Find z
Question:
z^3+i=0
My attempt:
z^3=-i
use z^n=|z|^(n) x e^((i)(n)(theta))
n = 3
|z|=1
theta = -pie/2
Is this correct?
 
Physics news on Phys.org
if z=i

z^2=-1 z^3=-1*i >>-i
 
… one step at a time …

Ry122 said:
z^3+i=0
My attempt:
z^3=-i
use z^n=|z|^(n) x e^((i)(n)(theta))

Hi Ry122! :smile:

You must be much more logical, or you'll make mistakes. :frown:

Do it one step at a time.

You know z^3=-i.

So - first step - write -i in the form r.e^(i theta).

What is it?

Then divide theta by 3. :smile:

Oh … and how many different solutions are there? :rolleyes:
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
Back
Top