Help Me To: |
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Eligible Content M3.B.2.1.2
Help Me To: |
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Find the perimeter of a figure drawn and labeled (with the same units throughout)
Did You Know?
The perimeter is the distance around a figure. You can add up the sides to get the perimeter.
Check What You Know First
| What the perimeter is of this figure? |
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| What the perimeter is of this figure? |
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What is the perimeter of a rectangle with these dimensions? |
Length = 7 inches Width = 4 inches. |
Key Vocabulary
The perimeter is the distance around a figure.
A rectangle is a plane figure with opposite sides that are
equal and parallel, and with
four right angles.
A square is a
polygon with 4 equal sides and 4 right angles.
Congruent is
having the same size or shape.
A plane figure is a closed figure that lies on a flat surface and is all in one plane.
A polygon is a closed figure with straight sides.
A right angle is an angle that forms a square corner and has a measure of 90 degrees.
Learn About It Now
Calculating the Perimeter of a Rectangle
The perimeter of a rectangle is the distance around the outside
of the rectangle.
A rectangle has four sides with opposite sides being
congruent.
The formula for finding the perimeter is:
Side A + Side B + Side A + Side
B or
Length + width + Length +Length
This could also be stated as:
2 x Side A + 2 x Side B or 2 x (Side A + Side B) or
2 x length + 2 x width
One final way to find perimeter is:
2 x (length + width)
The shortened formulas look like this:
Perimeter (P) = l + w + l + w or
Perimeter (P) = (2 x l) + (2 x w) or
Perimeter (P) = 2 x (l + w)
Let’s look at the following problem.
The length of each side is 6 units and the width of each side is 3.
Let’s use the formula to figure out the perimeter. You have to
add up all the sides.
P = length + width + length + width
P = 6 + 3 + 6 + 3 = 18
The perimeter of the rectangle is 18 units.
You can also use this formula:
P = (2 x l) + (2 x w)
Note that the perimeter of a rectangle is 2 times the length
plus 2 times the width
or (2 x 6) + (2 X 3) = 12 + 6 = 18 units.
Try it one more way by using this formuia:
P = 2 x (l + w)
The perimeter of a rectangle can also be obtained by adding
the length and width
and multiplying both by 2.
2 x (6 + 3) = 2 x 9 = 18
In the following problem there are no numbers. However there are squares
to count.
You have to first count the squares on 1 side which is 3. Then
count the 5 squares
on the other side.
The width of each side is 3 squares or units. The length of each side
is 5
squares or units.
Now you can use the formulas to find the formula.
P = length + width + length + width
P = 5 + 3 + 5 + 3 = 16
P = (2 x l) + (2 x w)
P = (2 x 5) + (2 x 3) = 10 + 6 = 16
or
P = 2 x (l + w)
P= 2 x (5 + 3) = 2 x 8 = 16
The perimeter of this figure is 16 units.
In the following problem, there is no picture, only the dimensions of a rectangle.
However,
you can put the numbers into the formula to figure out what the perimeter is.
In
a rectangle the opposite sides are congruent, so you will have 2 lengths of
7 inches
and 2 widths of 4 inches.
Again you can do it 3 ways.
What is the perimeter of a rectangle with these dimensions: Length
= 7 inches
Width = 4 inches.
Method 1:
P = length + width + length + width
P = 7 + 4 + 7 + 4 = 22
inches
Method 2:
P = (2 x l) + (2 x w)
P = (2 x 7) + (2 x 4) = 14 + 8 = 22 inches
Method 3:
P = 2 x (l + w)
P= 2 x (7 + 4) = 2 x 11 = 22
The perimeter is 22 inches.
Calculating the Perimeter of a Square
Calculating the perimeter of a square is easy since all the sides are equal.
In this problem, each side is 8 feet.
The formula for finding the perimeter of a square is:
P = length + width + length + width
P = 8 + 8 + 8 + 8 = 32
or
P = (2 x l) + (2 x w)
P = (2 x 8) + (2 x 8) = 32
or
P = 4 x s (s = the number of the sides)
P = 4 x 8 = 32
More Practice With Finding the Perimeter of a Number
CLICK HERE to
practice calculating perimeter of a rectangle.
CLICK HERE to
practice calculating perimeter of a square.
Websites to Check Out For Extra Practice
http://www.beaconlearningcenter.com/WebLessons/
Click on "Adam Ant"
Geometry – Area and Perimeter
http://www.mathplayground.com/InteractiveGeometry.html
Shape Surveyor – Finding
Perimeter and Area
http://www.funbrain.com/poly/index.html
Instructions
You will be shown a rectangle with the dimensions labeled.
You must calculate the area or perimeter of the rectangle.
For each problem you get correct, you will receive a piece of an archeological
puzzle.
The game is over when you get all the puzzle pieces.