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Definition of a Line Lines are used and seen everyday! There are lines everywhere. When people think of a line, they usually think of a solid bar. The truth is that lines are made up of an infinite number of points that stretch infinitely in opposite directions. If you ask someone to draw a line, the will probably draw something like this: . This is wrong. A line, remember, stretches infinitely in opposite directions. Vertical and Horizontal Lines Before getting to the complicated world of graphing lines with equations, first we will graph simple lines. A Coordinate Plane is used to graph lines on. It consists of a horizontal axis called the x-axis, and a vertical axis called the y-axis. The two lines meet at a point called the origin. The graph of X = 5 ( See fig. 1) would be a vertical line even though the x - axis is a horizontal line. The same for the graph of y = 5 ( See fig. 2), except that line would be horizontal while the y - axis is vertical. Graphing To graph a point on the coordinate plane, you need an ordered pair. An ordered pair is expressed as follows: (3, 4). The numbers inside tell you where to place the point. The first number represents the x-axis.