Lesson 1: Perimeter and Circumference - Perimeter

   Constructing Knowledge

The sidewalks around a city block create a perimeter around the buildings or neighbourhood they are surrounding.

Perimeter is the distance around a 2-D shape. To calculate perimeter of a shape, determine the sum of the linear distance around a 2-D shape. There may be instances where multiplication can be used, but only when there are multiple sides of a 2-D shape that are the same length.

Prior to determining the perimeter of a shape:

  • ensure you have the lengths of all sides of the shape.
  • make sure the sides lengths are all in the same unit of measure.

Abbreviations are frequently used when showing work for perimeter. Some common abbreviations are:

  • P for perimeter
  • s for side
  • l for length
  • w for width

EXAMPLE 1

Determine the perimeter of this triangle.



Solution


perimeter = side + side + side
= 5 cm + 5 cm + 5 cm
= 15 cm

or

Alternate solution: Use multiplication because all the sides are the same length.

perimeter = 3 sides
= 3 × 5 cm
= 15 cm

The perimeter of the triangle is 15 cm.

   Multimedia

A video describing perimeter is provided.



EXAMPLE 2

Determine the perimeter of the rectangle.



Solution


perimeter = length + length + width + width
= 20 ft + 20 ft + 10 ft + 10 ft
= 60 ft

or

Alternate solution: Use multiplication because pairs of sides are the same length.

perimeter = 2l + 2w
= (2 × 20 ft) + (2 × 10 ft)
= 60 ft

The perimeter of the triangle is 60 ft.


Now, it is your turn! Complete the questions in your Chapter 7, Lesson 1 Practice Makes Perfect that refer to Perimeter.



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