1. Estimate the angle?
Now measure the angle?
150º

2. Estimate the angle?
Now measure the angle?
215º

3. Constructing triangles
Aim: To construct triangles using a protractor.
60º

4. Draw a triangle with one side 6cm and angles at each end of 30º and 70º.
Mark 70º
Mark 30º
6 cm

5. Draw a triangle with a side 12 cm and side 9 cm
with an angle of 75º between them.
Mark 75º
12 cm

6. Three ways to construct triangles.
When constructing triangle we need a combination of angles of lengths.
We can construct triangles with a compass if we have the lengths of the 3 sides (S S S).
We can construct triangle using a protractor if we have the length of 1 side and the measurement of 2 angles ( A S A ).
We can construct triangle using a protractor if we have the length of 2 sides and the measurement of 1 angles ( S A S ).
Note: To construct triangles, we need to know the length of at least 1 side plus 2 other pieces of information.

7. Task and Homework
Construct the following triangle:
S S S Triangles
5cm 7cm 9cm
6cm 6 cm 4cm
10cm 8cm 7cm
6cm 8cm 10cm
7cm 7 cm 7 cm
A S A Triangles
40º 7cm 50º
45º 6 cm 45º
20º 8cm 100º
60º 8cm 60º
110º 7 cm º
A S A Triangles
7cm 50º 4 cm
6 cm 45º 6 cm
8cm 100º 6 cm
8cm 60º 8 cm
7 cm º 6 cm