1-8: Perimeter, Circumference, and
Area
Objectives for this Lesson
• Find the perimeter of a polygon.
• Find the circumference of a circle.
• Find the area of a polygon and of a circle.
Remember what a
is?
: A closed plane figure (it lies in a plane) formed
by 3 or more segments.
• all segments are connected at their endpoints
• segments don’t cross
a polygon
not a polygon
not closed
not a polygon
segments cross
Names of Polygons
Name a polygon by its number of sides (and angles)
# of sides
3
4
5
6
7
8
9
10
11
12
Name
Triangle
Quadrilateral
Pentagon
Hexagon
Heptagon
Octagon
Nonagon
Decagon
Hendecagon
Dodecagon
:
All sides and angles
congruent
Perimeter and Circumference
: Length (distance) around a polygon.
• Add the lengths of all the sides
𝑝𝑒𝑟𝑖𝑚𝑒𝑡𝑒𝑟 = 𝑠𝑢𝑚 𝑜𝑓 𝑎𝑙𝑙 𝑠𝑖𝑑𝑒 𝑙𝑒𝑛𝑔𝑡ℎ𝑠
: Length (distance) around a circle.
𝐶 = 2𝜋𝑟
Area
: The number of square units enclosed by a figure.
• Always has units squared
𝐴𝑠𝑞𝑢𝑎𝑟𝑒 = 𝑠2
𝐴𝑟𝑒𝑐𝑡𝑎𝑛𝑔𝑙𝑒 = 𝑏ℎ
𝐴𝑡𝑟𝑖𝑎𝑛𝑔𝑙𝑒
1
= 𝑏ℎ
2
𝐴𝑐𝑖𝑟𝑐𝑙𝑒 = 𝜋𝑟2
Finding Perimeter in the Coord. Plane
Use the distance formula to find any lengths that
aren’t vertical or horizontal.
𝒅=
⋅
⋅
𝑃(3,6)
𝑆(3,3)
⋅
𝐷 (7,3)
𝒙𝟐 − 𝒙𝟏
𝟐
+ 𝒚𝟐 − 𝒚𝟏
𝟐
Do the 1-8 assignment in MathXL