1. Appendix B: Coordinate System and Lines
There are different coordinate systems.
Rectangular (Cartesian) coordinate system
Polar coordinate system ……
One geometric object can be easily described in one coordinate system but not in another one. That is why there are quite a few coordinate systems out there.

2. Throughout this course, we only use Cartesian coordinate system:
One horizontal line pointing right is called the x-axis
One vertical line pointing upward is called the y-axis
The intersection point is called the origin, denoted by O
These two lines divide the plane into four quadrants

3. There is a 1–1 correspondence between ordered pairs of real numbers and points on the plane.

4. P2(x2, y2), denoted by |P1P2|, is given by
The distance between two points P1(x1, y1) and
P2(x2, y2), denoted by |P1P2|, is given by

8. Equations of lines