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Co-ordinates
These are a way of plotting a point on a graph.
To plot the point A with co-ordinates (2,3) we start at 0 and move two places to the right and three places up on the x and y axis.
Example of plotting points:
Plot the points A(2,3), B(5,1), C(-3,-2), D(2,-3) and E(-1,2) on the graph below.
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Note: The first number in the bracket indicates the movement right or left.
The second number indicates the movement up or down.
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Graphs (Simple)
The graph of a line can be given in the form of an equation.
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Graphs of straight lines
An example of an equation of a straight line is y=2x.
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To Plot the Graph of the equation
We can plot this graph by working out the co-ordinates. To do this we make up values for x and substitute them into the equation to find the values of y. The results are put in a table, as below.
| Table of co-ordinates for y=2x |
| x |
y |
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| -1 |
-2 |
y = 2 x -1 = -2 |
| 0 |
0 |
y = 2 x 0 = 0 |
| 1 |
2 |
y = 2 x 1 = 2 |
| 3 |
6 |
y= 2 x 3= 6 |
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Plotting these co-ordinates and drawing a line through them gives the graph of y=2x below.
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y=2x |
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Some simple equations whose lines should be known.
1) y lines, these are horizontal lines. For example y=2 y=-3 y=0.
2) x lines, are vertical lines For example x=5 x=10 x=0.
3) y=x and y=-x are diagonal lines.
4) x+y lines, for example x+y = 1 passes through 1 on the x axis and 1 on the y axis.
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| Graphs of x and y lines |
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| Graph of y=x and y=-x |
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| Graph of x+y = 4 and x+y = 1 |
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