# Homework Help: Complex expressions

1. Oct 11, 2013

### ENGR_student

Hello I'm studying complex numbers for class and the question is stated as:
Let z=1+2i
Find:
a) 1/z^2
b) 1/z^3

I was thinking just to multiply by the conjugate (1-2i)^2 for (a) and similarly for (b).
Would that be correct in solving it?

2. Oct 11, 2013

### Staff: Mentor

You can do that, right.
Alternatively, calculate 1/z first, and then calculate powers of that.

3. Oct 11, 2013

### ENGR_student

Oh thank you!
I apologize if I put it in the wrong thread!

4. Oct 12, 2013

### skiller

Firstly, let's establish what you are actually asking.

For example, the way you wrote it, 1/z^2 = $\frac{1}{z^2}$, NOT $(\frac{1}{z})^2$

EDIT: Please ignore. Complete brain-fart by me there!

Last edited: Oct 12, 2013
5. Oct 12, 2013

### Staff: Mentor

Where is the difference?

6. Oct 12, 2013

### skiller

Thanks. I simply cannot believe what I wrote in my previous post.

I blame lack of sleep...:zzz:

7. Oct 12, 2013

### HallsofIvy

Surely there must be some way to completly delete a post so that those of us who post a really stupid idea can pretend it never happened!?
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