Straight lines

14

Contents:

A Vertical and horizontal lines [7.6]

B Graphing from a table of values

C Equations of lines

(gradient-intercept form) [7.6]

D Equations of lines (general form) [7.6]

E Graphing lines from equations [7.6]

F Lines of symmetry [7.8]

Opening problem

#endboxedheading

On the coordinate axes alongside, three lines are drawn.

How can we describe using algebra the set of all points

on:

² line (1) ² line (2) ² line (3)?

InChapter 12we learnt how to find the gradient of a line segment. In this chapter we will see how the

gradient can be used to find theequationof a line.

Theequation of a lineis an equation which connects thexandyvalues for every point on the line.

To begin with we consider horizontal and vertical lines which are parallel to either thexory-axis.

A VERTICAL AND HORIZONTAL LINES [7.6]

O

y

x

2

2

-2

-4

-6 -4 -2 2 4 6

(2)

(1) (3)

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Y:\HAESE\IGCSE01\IG01_14\297IGCSE01_14.CDR Friday, 26 September 2008 10:33:48 AM PETER