CBSE NCERT 8th Introduction of Graphs
The mathematician who introduced graph was Rene Descartes, a French Mathematician in early 17th century. Coordinate axes: The position of a point in a plane is determined with reference to two fixed mutually perpendicular lines, called the coordinate axes. To mark a point, we always write the xcoordinate (or the number on the horizontal axis) first and then the ycoordinate (or the number on the vertical axis). The first number of the pair is called the xcoordinate or abscissa. The second number of the pair is called the ycoordinate or ordinate. Origin is the point of intersection of xaxis and yaxis. Let us consider the point P (4, 6). It is 4 units away from the right side of the yaxis and 6 units above the xaxis. Then the coordinate of the point P is (4, 6). Example Plot the following points on a graph paper and find out where do they lie? (i) A (7, 0) (ii) B (– 5, 0) (iii) C (0 , 4) (iv) D (0, – 3) Solution: Draw the x and y axes. Mark the units along the x and y axes with a suitable scale. (i) To plot the point A (7, 0) Here, the xcoordinate of A is 7 which is positive and the Ycoordinate of A is zero. Hence the point A (7, 0) lies on the xaxis. Start at the Origin. Move 7 units to the right along the xaxis and mark it. (ii) To plot the point B (–5 , 0) Here, the xcoordinate of B is –5 which is negative and the ycoordinate is zero. Hence the point B (–5 , 0) lies on the xaxis. Start at the Origin. Move 5 units to the left along the xaxis and mark it. (iii) To lot the point C (0 ,4) Here, the xcoordinate of C is zero and the ycoordinate of C is 4 which is positive. Hence the point C (0 , 4) lies on the yaxis. Start at the Origin. Move 4 units up along the yaxis and mark it. (iv) To plot the point D (0 , –3) Here the xcoordinate of D is zero and the ycoordinate of D is –3 which is negative. Hence the point D (0, – 3) lies on the yaxis. Start at the Origin. Move 3 units down along the yaxis and mark it. 



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