In this lesson you’ll learn about the basics and concepts of perimeter and circumference,
and how to find the pperimeter and circumference of geometric shapes. The presentation
covering such content will be done by the instructor in own handwriting, using
video
and with the help of several examples with solution. This will help you understand and master
the basics and formulas of important geometry applications in this area, and how to apply
them to find solution.
You’ll come across in geometry using two terms ‘Perimeter and Circumference’.
The basic difference between the two can be understood like: ‘perimeter’ refers
to the length of the outline of a shape with defined starting and end points and
‘circumference’ is the length of outline of a circle. In case of a circle, since
the shape is curve and not straight line governed boundaries, total length of
outline can not be found simply by adding up the border. How to determine these
two is explained here after for regular as well as irregular shapes.
(More text below video...)
(Continued from above)
Regular shapes
The perimeter of a figure is the distance around it. You measure perimeter in units of lengths,
such as kilometers, meters, centimeters, millimeters, inches, feet, yards, miles etc. To find
the perimeter of a closed figure made up of line segments, add up the lengths of the line
segments. E.g. find the perimeter of the closed figure (Fig: 1):
To find the perimeter, add the length of the four sides, i.e. (8+5+7+4) = 24 in.
The circumference of a circle is determined by the formula: Circumference =
2r,
where 'r' is the radius of the circle. Notice that larger the radius of the circle,
larger is the circumference. E.g. find the circumference of the circle in the
diagram (Fig: 2) above:
Circumference =
2r
= 2**2
= 12.57 in.
The value of
is approximately 3.14159265358979323846...
Note: The diameter of a circle is twice the radius. The number
is the ratio of the
circumference of a circle to the diameter.
Given the circumference of a circle, you
can find the diameter using the formula: Circumference
= *d
or
*2*r.
For example,
Given: the circumference of a circle 24
in., find out the diameter of this circle?
It can be determined by using the formula: Circumference
= d.
Thus d= Circumference/
= 24 / = 24 in.
Irregular shapes
You may come across some shapes where it is a combination of rectangles, squares, circles,
triangles, rhombus etc, or part thereof. In such cases perimeter can be found out by
breaking up the irregular shapes into components suitably and then individual part
perimeters are added up to find the total length of the boundary. E.g. in Fig: 3,
the original shape is made up of two different shapes (Rectangle and Triangle).
Remember:
• perimeter is not the same as area (area is the region in the enclosed boundary).
• likewise circumference is not the same as area Perimeter in case of circle.
• diameter of a circle is twice the radius.
The video above will explain more in detail about Perimeter and Circumference,
with the help of several examples.
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r,
where 'r' is the radius of the circle. Notice that larger the radius of the circle,
larger is the circumference. E.g. find the circumference of the circle in the
diagram (Fig: 2) above: