The system used for describing the position of a point in a plane with reference to two mutually perpendicular lines is called cartesian or rectangular coordinate system. Coordinate axes: Let us draw a horizontal line on a graph paper and draw a vertical line intersecting the horizontal line. The horizontal line is called x -axis and vertical line is called y -axis. The two lines taken together are called coordinate axes. Origin: The point of intersection of x-axis and y -axis are called origin. Quadrant: The coordinate axis divide the plane of graph paper into 4-regions called quadrant. Coordinate of a point: Let A(x, y) be the point in a plane. x=distance of point from y-axis. y=distance of point from x-axis. Convention of sign: I quadrant →x > 0, y > 0 II quadrant →x < 0, y > 0 III quadrant →x < 0, y < 0 IV quadrant →x > 0, y < 0