# Inequality and complex numbers

1. Sep 17, 2009

### oddiseas

1. The problem statement, all variables and given/known data

b)show that if |z|>=3 then the following inequality holds

2. Relevant equations

|z|>=3 now for this to hold b must be <=0 which gives the following:
|e^iz|=e^b(cosa+isina) and taking the magnitude yeilds (e^2b)^1/2
I dont know where to go next.

Last edited: Sep 17, 2009
2. Sep 17, 2009

### LCKurtz

You are having trouble with the first part. What are a and b? Are you writing
z = a + ib. If so, you should say so.

This equation |e^iz|=e^-b(cosa+isina) can't be correct because you have a real number on the left and a complex number on the right.

The "inmaginery" (that's imaginary) part of what is one? And why is it 1? Do you know how to compute the magnitude of a complex number?

"provided b is <=0". You are given Im(z) >= 0.

Back to the drawing board.

3. Sep 17, 2009

### Staff: Mentor

Please post the exact problem you are supposed to solve. The following makes no sense:
What following inequality? It doesn't appear in either your original post or the edited post.