Thread: The Complex Exponential And Regions in the Complex Plane

Hello all, I have done a few questions that I need corrected.

1.) Sketch the region of the complex plane defined by Im (z^2) = 2 for pi/8 < arg (z) < 3pi/8

my solution: I let z = x + iy, then found z^2 and the imaginary parts of z^2 which gave me a graph shape of 1/x. the region defined by the angle is in the first quadrant and only a small bit of that curve is included.

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2.) z = 1/4 - [root(3) / 4]i

a) Write z in exponential polar form for angles between -pi and pi

my solution: 1/2 * e ^ i (pi/3)

b) Calculate (1/z) ^ 9

my solution: -2 * 2^8 + 0i

__________________________________________________ ______________________

3.) Use the complex exponential to express sin^3(theta) as a sum of sines or cosines of multiples of theta.

My solution: -1/i sin(3 theta) + 3/i cos (theta)
__________________________________________________ ______________________

Thank you in advance.

Originally Posted by andrew2322

Hello all, I have done a few questions that I need corrected.

1.) Sketch the region of the complex plane defined by Im (z^2) for pi/8 < arg (z) < 3pi/8

my solution: I let z = x + iy, then found z^2 and the imaginary parts of z^2 which gave me a graph shape of 1/x. the region defined by the angle is in the first quadrant and only a small bit of that curve is included.

__________________________________________________ ______________________

2.) z = 1/4 - [root(3) / 4]i

a) Write z in exponential polar form for angles between -pi and pi

my solution: 1/2 * e ^ i (pi/3)

b) Calculate (1/z) ^ 9

my solution: -2 * 2^8 + 0i

__________________________________________________ ______________________

3.) Use the complex exponential to express sin^3(theta) as a sum of sines or cosines of multiples of theta.

My solution: -1/i sin(3 theta) + 3/i cos (theta)
__________________________________________________ ______________________

Thank you in advance.

1. Are you sure it didn't say

2. a) It's clear that is in the fourth quadrant, so can not possibly be .

b) This is easiest to evaluate if you have evaluated part a) correctly...

Hello Prove it. I checked the question again and it says arg (z) not arg (z^2)

also, for part 2a) I realise my careless mistake, I was meant to type - pi/3.

due apologies.

Sorry Prove It and others. The Im (z^2) = 2, i forgot to include the = 2 part. very sorry.

I have edited the original post to include this correction.

Originally Posted by andrew2322

Hello Prove it. I checked the question again and it says arg (z) not arg (z^2)

also, for part 2a) I realise my careless mistake, I was meant to type - pi/3.

due apologies.

Then is correct.

is part B correct?

Originally Posted by andrew2322

is part B correct?

You tell me. , so what is ?

2^9 e ^3pi?

which is equivalent to 2^9 e^pi which is 2^9 (cos(pi) +isin(pi)) which is -1 * 2^9?

Originally Posted by andrew2322

2^9 e ^3pi?

Correct, but don't forget the 'i':

Cool, thanks for the heads up. I really have to stop doing that haha.

Would you happen to have any clue on how to do Q1)? I reposted it because this one got quite messy and still have yet to receive a response.