2. What is Perimeter?
Suppose you need to put a ribbon border around a
picture .
How would you decide how long the ribbon needs to
be?
One way would be to measure each side and add them
together!
The sum of all the sides together is called the
Perimeter.
3. Perimeter of a Rectangle
To find the perimeter of a rectangle, add all the sides.
Perimeter = length + length + width + width
*Remember* in a rectangle, opposite sides are equal.
That means we can rewrite the formula as:
P= 2l + 2w
Length
Length
WidthWidth
4. Practice
What is the Perimeter of the following
rectangle?
P= 2l + 2w
P=2(10)+2(5) = 20 +10 = 30 cm
5 cm
10 cm
10 cm
5 cm
5. Practice Perimeter
Click on the right answer!
1.
A. 30
B. 46
C. 23
D. 165
A. 150
C. 236
B. 86
D. 193
15
88
15 75
43
2.
6. Perimeter of a Polygon
How could we find perimeter for other shapes?
If all sides are given, we can add them up!
P= 8 + 8 +3 + 3 +11
P= 33
8
11
8
3
3
9. Perimeter and Algebra
Using what we learned about perimeter, we
could be able to solve for a missing side:
Given that the
Perimeter of the
polygon is 35, find
the value of x.
35=5 + 7 + 4 + 9 + x
35=25 + x
10=x
x
7
9
4
5
10. Perimeter and Algebra
Perimeter could also be written in terms of a variable. Let’s see how:
If we add all the sides we
get:
P = 3x + 3x + x + 1 + x + 1
P = 8x + 2
If we were told the sum of all sides is 26, how could we find each side?
We know 8x + 2 = Perimeter (sum of all sides)
So, 8x +2 = 26
If we solve for x we should get, x = 3
Thus, the length of 3x = 3(3) =9
and the width of x+1 = 3 +1 =4
3x
3x
X+1 X+1
11. Practice
Given that the Perimeter of the rectangle is 86,
find the measure of each side.
2x+3
2x+3
2x 2x
A. 10 and 20
B. 20 and 23
C. 10 and 13
D. 20 and 13
12. Practice
Given the sum of the sides of the regular
hexagon is 125 , find the value of x
X + 5 A. 10
B. 120
C. 50
D. 20
