In the preceding section, you found that positive or negative is sufficient for the direction of a vector in one dimension. However, in 2D and 3D, positive or negative just isn't enough. There are two different forms for describing a vector in 2D: polar coordinates and Cartesian coordinates. Polar coordinates are a little more intuitive, so let's look at them first.
where is the magnitude of A and θ is the direction.
Figure 4.2 illustrates polar coordinates.