The modulus and argument of a complex number.

[list=1] [*] Move [color=#0000ff][math]z[/math][/color] and see how the modulus [color=#ff0000][math]|z|[/math][/color] and the argument [color=#006400][math]\arg(z)[/math][/color] change. [*] In particular, observe that [color=#006400][math]0\leq\arg(z)<2\pi[/math][/color] and [color=#ff0000][math]|z|\geq0[/math][/color] [/list]