Argument of a Complex Number

Rarely Tested

Argument of a Complex Number

## Formula

For:

$$z=x+iy$$

the argument $$\theta$$ satisfies:

$$\tan\theta=\frac{y}{x}$$

The general argument is:

$$\arg(z)=\theta+2n\pi,\qquad n\in\mathbb Z$$

The principal argument is generally denoted by:

$$\operatorname{Arg}(z)$$

with:

$$-\pi<\operatorname{Arg}(z)\le\pi$$

## Conditions / Special Cases

For $x>0$ and $y>0$:

$$\operatorname{Arg}(z)=\tan^{-1}\left(\frac{y}{x}\right)$$

The correct quadrant must always be considered when determining the argument.

For positive real numbers:

$$\operatorname{Arg}(z)=0$$

For negative real numbers:

$$\operatorname{Arg}(z)=\pi$$

For positive imaginary numbers:

$$\operatorname{Arg}(z)=\frac{\pi}{2}$$

For negative imaginary numbers:

$$\operatorname{Arg}(z)=-\frac{\pi}{2}$$

## Usage

- Used to determine the angular position of a complex number in the Argand plane.

Question 1

Let $$z = 1 + i$$. Define a new complex number $$z_1$$ as follows:

$$z_1 = \frac{1 + i\bar{z}}{\bar{z}(1 - z) + \frac{1}{z}}$$

Then the value of $$\frac{12}{\pi} \arg(z_1)$$ is equal to:

Question 2

Let $$z=a+ib$$ where $$a,b\in\mathbb{R}.$$ If $$\arg(z-2)=\arg(z+4i)$$ and $$|z-2|=2|z+4i|,$$ then the value of $$a+b$$ is:

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