Finding the perimeter of triangles and polygons

Exercise: Find the perimeter of polygons

Find the perimeter of the following polygons. If you like, you can draw them on a piece of paper first.

Polygon 1

The lengths of all four sides have been given to you.

Polygon 2

Even though it is a strange looking shape, once again, the lengths of all the sides have been given to you.

Polygon 3

Be a bit careful with this one. Remember the markings on each side tell you that they are equal in length. Do you know the lengths of all the sides?

Polygon 4

You are told that this shape is a rectangle. What do you know about the lengths of the opposite sides of a rectangle? Do you know the lengths of all the sides now?

Polygon 5

This is an irregular polygon. You have not been given the lengths of all the sides but can you work out what the lengths of the sides you have not been given are?

Answers: You should have gotten the following answers.

• Polygon 1:  Perimeter = 17 cm + 16 cm +22 cm +16 cm = 71 cm
  
• Polygon 2: Perimeter = 9 cm + 7 cm + 3 cm + 8 cm + 4.5 cm + 8 cm = 39.5 cm
  
• Polygon 3: All three sides are the same length so the perimeter = 6 cm + 6 cm + 6 cm = 18 cm
  
• Polygon 4: The opposite sides of a rectangle are the same length so the perimeter = 8 cm + 5 cm + 8 cm + 5 cm = 26 cm
  
• Polygon 5: Here you had to find the length of the missing sides. The one side has a length of 10 cm - 6 cm = 4 cm. The other side has a length of 5 cm - 2 cm = 3 cm. So the perimeter = 6 cm + 3 cm + 4 cm + 2 cm + 10 cm + 5 cm = 30 cm