absolute value

The absolute value of a number is its distance from zero.

Formally,
for a real number $a\in \mathbb{R}$, the absolute value of $a$ is

Some properties of the absolute value include

1. $|ab|=|a||b|$
2. $|a{|}^2=a^2$
3. if $c\ge 0$, then $|a|\le c⟺-c\le a\le c$
4. $-|a|\le a\le |a|$
5. $|a+b|\le |a|+|b|$ (triangle inequality)