Constructing Triangles
The old way

Given two sides and the included angle (SAS)

Mark exact length 10 cm using a ruler and short marker lines

Eg 10 cm side, 5 cm side and 45° angle between

Draw a line a bit longer than needed.

Use a protractor to mark

a 45° angle

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

10 cm

A

B

C

Constructing triangles the old way

Remove the protractor and

label the line A C

Draw a line using a ruler

from A through the 45°

marker longer than

5 cm

Measure and mark off

the length 5 cm and label

point B

Join B to C to complete the triangle

10 cm

5 cm

Constructing Triangles the old way

Construct a triangle given all three sides (SSS)

eg 13 cm, 12 cm and 5 cm.

Draw a base more than 13 cm long

Mark off 13 cm using short lines

Label A C

Use a compass to draw an arc

centre A radius 12 cm

Use a compass to draw an arc

centre C radius 5 cm

Label point B where the arcs

cross, join AB and AC

A

B

13 cm

C

12 cm

5 cm

Using a modern method

Use a drawing program

Draw a line by specifying its

length to 1 tenth 1 mm and

the program will draw it.

7.38cm

Rotate a line through any angle

by giving the centre of rotation

and the angle

Centre of rotation

23.7°

2003-10-16T09:22:13