Cambridge International Mathematics

Straight lines (Chapter 14) 301

y=mx+c is thegradient-intercept formof the equation of a line

with gradientmandy-interceptc.

For example: The illustrated line has gradient=

y-step

x-step

=^12

and they-intercept is 1

) its equation is y=^12 x+1.

We can find the equation of a line if we are given:

² its gradient and the coordinates of one point on the line, or

² the coordinates of two points on the line.

Example 2 Self Tutor

Find the equation of these lines:

ab

a

The gradient m=

y-step

x-step

=^13.

They-interceptc=2.

) the equation is y=^13 x+2

b

The gradient m=

y-step

x-step

=¡ 63 =¡^12.

They-intercept c=3.

) the equation is y=¡^12 x+3

EQUATIONS OF LINES

(GRADIENT-INTERCEPT FORM) [7.6]

C

x

y

1

1

2

O

O

y

x

36

3

3

1

O

y

x

36

3

6

-3

O

y

x

36

3

O

y

x

36

3

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Y:\HAESE\IGCSE01\IG01_14\301IGCSE01_14.CDR Friday, 26 September 2008 1:38:25 PM PETER