In this chapter, the Cartesian coordinate system is introduced. The distance between points, midpoints, perpendicular/parallel lines and angles between two lines are covered. The general and point slope form of the equation of the straight line are also covered. 1.2 Lesson Learning Outcomes By the end of this lesson, you should be able to; 1.2.1 Carry out operations on the Straight Line. 1.2.1 The Straight Line In this work the geometrical problems considered are those that are presented on two dimensional plane only and it is therefore important at this point to discuss the plane. Consider any plane with a point denoted by O, which we call the point of reference or the origin. Let line X be horizontal and pass through O and line Y be vertical and pass through O. The horizontal line X is referred to as the x-axis and the vertical line Y is the y-axis. Distance measured from the y-axis is referred to as an abscissa and it is positive if measured to the right and negative if measured to the left. A vertical distance from the x-axis is called a y-ordinate and it is positive if measured above the x-axis and negative if measured below the x-axis. Any point on the plane can described by its abscissa and its ordinate as P(x, y), for any point P. The symbol (x, y) represents the coordinates of the point, where x is the abscissa and y the ordinate and it is also referred to as the Cartesian coordinates of P.