Page 321 - Math Smart - 7
P. 321
Constructing regular polygons
Investigate!
Let us investigate the size of the internal angles of a pentagon,
a) Measure the sizes of and Zd in the regular pentagon. What is the sum
of the interior angles of the pentagon?
/.a =
^c = zlc/ = zle =
Conclusion
In a regular polygon, all sides are of length and all angles are
of size.
b) We can also find the sum of the internal angles by dividing the polygon
into triangles.
3 X 180° = 540°
sum sum
sum
Conclusion
Each internal angle = (180° x ) 5
We can make use of the size of each internal angle of regular polygons when we
construct regular polygons.
Example 12
Construct a pentagon with sides of length 40 mm and internal angles of 108°.
Use your pencil and ruler to draw a line 40 mm long.
40 mm
