URGEN taking the power of complex exponential

kougou
Messages
80
Reaction score
0

Homework Statement



e^(i*2pi*1/15) is equal to ( e^(i*2pi) )^(1/15) = (1)^(1/15)=1

Why this is false?

Homework Equations



((A)^(b))^c=A^(b*c)=A^(bc). Why this isn't the case for complex exponential?

The Attempt at a Solution

 
Physics news on Phys.org
kougou said:

Homework Statement



e^(i*2pi*1/15) is equal to ( e^(i*2pi) )^(1/15) = (1)^(1/15)=1

Why this is false?

Homework Equations



((A)^(b))^c=A^(b*c)=A^(bc). Why this isn't the case for complex exponential?

The Attempt at a Solution


Because it isn't. The rule (A^b)^c=A^(bc) doesn't hold for complex exponents. As your example shows.
 
Dick said:
Because it isn't. The rule (A^b)^c=A^(bc) doesn't hold for complex exponents. As your example shows.

But why?
When I use take the positive integer power of complex exponential, it works. What's the rule?
 
kougou said:
But why?
When I use take the positive integer power of complex exponential, it works. What's the rule?

If b and c are integers you should be safe. If A is a positive real and one of b or c is an integer, that should also be ok. Otherwise, I think it's dangerous.
 
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