# What is the absolute value of -a?

The absolute value of $\left(- a\right)$ is
$\left\{\begin{matrix}a \text{ if " a>=0 \\ -a " if } a < 0\end{matrix}\right.$
If $a = - 7$ then $\left\mid - a \right\mid = \left\mid - \left(- 7\right) \right\mid = \left\mid 7 \right\mid = 7 \left(= - a\right)$
If $a = + 4$ then $\left\mid - a \right\mid = \left\mid - 4 \right\mid = 4 \left(= a\right)$