Rotations on an Argand diagram

The point $A$ represents a fixed complex number $a$ where $\pi/4<\arg(a)<\pi/2$. The complex numbers $-ia$ and $-a$ are represented by the points $B$ and $C$ respectively.

On a single clearly labelled Argand diagram, mark the points $A$, $B$ and $C$.

Describe the geometrical relationship between

(a) $A$ and $B$, and

(b) $A$ and $C$.