Chapter 9
Math 7
Class Notes
Perimeters of Irregular Polygons
Vocabulary
Irregular Polygon
| o
| A polygon that is not uniform in shape or size
|
** IMPORTANT**
A line segment is identified by its endpoints with a line drawn over the letters:
AB
EXAMPLES
Make sure to show the formula used and each step to receive full credit.
Label, label, label
| 1.
| Find the perimeter of polygon ABCD |
5 in.
A
B
1 in.
C
2
in. 6 in.
D
P = AB + BD + DC + CA
P = 5 in + 6 in + 2
in + 1
P = 14
inches
| 2.
| Find each missing measure x, then find the perimeter of |
the polygon
Original Picture
4 in
4 in. 6 in.
x
2 in.
2 in.
To find a missing side, you must section the original picture into recognizable polygons – like squares, rectangles, etc.
Rectangles – opposite sides are equal
The dotted line was put in to help solve the problem.
2 in
4 in
2 in
4 in
4 in
6 in
x
2 in
2 in.
2 in
Rectangle II:
- The shorter side is 2 in, since opposite sides are equal,
the opposite side is
2 in
.
- The longer side is 6 in. – the opposite side is made up of the
original 2inches and the dotted line. To figure out the length
of the dotted line, take the 6 inches and subtract the original 2
inches an get
4 inches
.
Rectangle I:
- The two longer sides of this rectangle is
4 inches
.
Looking back
Rectangle II
, when the dotted line was put into place, it split the
original line
into two pieces – one we found to be
2 inches
. This makes the other half of the line
2 inches
.
Since opposite sides of a rectangle are equal
x = 2 inches
Back to the original problem:
| 3.
| Find each missing measure x, then find the perimeter of |
the polygon
We found:
x = 2 inches
P = 4 in + 4 in + 6 in + 2 in + 2 in + 2 in
= 20 in.
Textbook pages: 246-247
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