Page 624 - (DK) The Ultimate Visual Dictionary 2nd Ed.

A PPendix
Shapes: Plane

Two-dimensional shapes are termed plane (or flat) shapes. Plane areaS and
areaS and
and
areaS
shapes constructed with straight sides, as illustrated here, are PerimeTerS S
erime
T
P
PerimeTerS
er
called polygons. They are categorized according to the number of The formulae for
sides they have—for example, three-sided polygons are known as calculating the areas and
triangles. A polygon that has sides of perimeters of simple plane
shapes were devised by
equal length and internal angles of Classical Greek
equal size, such as a square, mathematicians.
is said to be regular.
r
d
Scalene Triangle iSoSceleS Triangle righT-angled Triangle
A triangle (three-sided A triangle with only two sides A triangle with one angle
polygon) with no and two angles equal. as a right angle (90º).
equal sides or angles.
circle
r = radius
d = diameter = 2 x r
Circumference = 2 x π x r
Area = π x r 2
(π = 3.1416)

equilaTeral Triangle Square rhombuS
A regular triangle. A regular quadrilateral. A quadrilateral with all sides
All angles are 60º. All angles are 90º. equal and two pairs of a
equal angles. c
h

b
Triangle
Height = h
Sides = a, b, c
Perimeter = a + b + c
recTangle Parallelogram TraPezium Area = ½ x b x h
A quadrilateral with four right A quadrilateral with two A quadrilateral with one pair
angles and opposite sides of pairs of parallel sides. of parallel sides.
equal length.

b

a

recTangle
Sides = a, b
PenTagon hexagon ocTagon
A five-sided polygon. A regular A six-sided polygon. A regular An eight-sided polygon. A Perimeter = 2 x (a + b)
pentagon is shown above. hexagon is shown above. regular octagon is shown above. Area = a x b
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