# Rotation formula Complex numbers

## Homework Statement

$$If arg(\frac{z-ω}{z-ω^2}) = 0, \ then\ prove \ that\ Re(z) = -1/2$$

## Homework Equations

ω and ω^2 are non-real cube roots of unity.

## The Attempt at a Solution

arg(z-ω) = arg(z-ω^2)
So, z-ω = k(z-w^2)
Beyond that, I'm not sure how to proceed. Using the rotation formula may also be required, but I'm not sure how to use it here.
Furthermore, I can sort of intuitively visualise the answer, but I'm not sure how to prove it analytically.

Last edited:

SammyS
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Homework Helper
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## Homework Statement

$$\text{If}\ \arg \left( \frac{z-ω}{z-ω^2} \right) = 0, \ \text{then prove that }\ Re(z) = -1/2$$

## Homework Equations

ω and ω^2 are non-real cube roots of unity.

## The Attempt at a Solution

arg(z-ω) = arg(z-ω^2)
So, z-ω = k(z-w^2)
Beyond that, I'm not sure how to proceed. Using the rotation formula may also be required, but I'm not sure how to use it here.
Furthermore, I can sort of intuitively visualise the answer, but I'm not sure how to prove it analytically.
If ω is one of the non-real cube roots of unity, then what is ω2, and how is it related to ω ?

1 + ω + ω^2 = 0
$$ω = e^\frac{i2\pi}{3}$$
How does that help?

SammyS
Staff Emeritus
Homework Helper
Gold Member
1 + ω + ω^2 = 0
$$ω = e^\frac{i2\pi}{3}$$
How does that help?
I was thinking in terms of the complex conjugate.

ω is the conjugate of ω^2.

Dick