Page 131 - MAT KS3 Y8 Cambridge CheckPoint

13 Graphs

In the 17th century the Frenchman René Descartes showed how to Key words
plot points on a grid and use this to draw lines and curves.
Make sure you learn and
In his honour we still call this method ‘Cartesian coordinates’.
understand these key words:
You have used positive and negative numbers as coordinates to equation
show points on a Cartesian grid. You know that equations involving line segment
x and y can correspond to lines and curves on such a coordinate midpoint
grid.

y
(–2, 3) 3 y = x
(4, 2)
2

1

–3 –2 –1 0 1 2 3 4 x

–1
y = –2
–2

–3 (1, –3)

Graphs also have many practical applications in real life. A graph
can be easier to read and understand than a table or chart.
This table shows the speed of a car at five-second intervals. The graph shows the same information.
Which is easier to understand?

Time (seconds) 0 5 10 15 20 25 30

Speed (km/h) 50 60 70 70 70 50 30

In this unit you will concentrate on straight-line graphs.
Two examples, y = −2 and y = x, are shown in
the diagram at the top of the page.
80
Speed (km/h) 60

40

20

0
0 5 10 15 20 25 30
Time (seconds)

13 Graphs 129