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CanadaON
Grade 6

Perimeter 2

Lesson

Adding it all together

Perimeter is all about the distance around the outside of our shape, so the perimeter of a triangle means adding $3$3 sides together. We can calculate the perimeter of equilateral, isosceles and scalene triangles, using what we know about those triangles, to help with missing values.

Let's see what features each of those triangles has, and how it can help us work out the perimeter of the triangle.

 

Worked Example

Question 1

Find the perimeter of the scalene triangle shown.

 

The power of the perimeter

This is where the perimeter helps us! If we know the perimeter of our triangle, we can work out how long one, or more, of the sides are. In fact, if we know the perimeter of an equilateral triangle, we can work out how long every side is. Let's look at using what we know to find missing values.

 

Worked Examples

Question 2

Find the side length $y$y indicated on the diagram. The perimeter of the shape is $54$54 cm.

Question 3

Find the side length of a triangle with a perimeter of $29$29 m given that two of the sides have lengths $8$8 m and $8$8 m.

 

Remember!

Different kinds of triangles mean we don't always need to know how long each side is to work out the perimeter. Using the features of each triangle type can help us with missing values.

Outcomes

6.M2.02

Solve problems requiring conversion from larger to smaller metric units

6.PA2.03

Solve problems that use two or three symbols or letters as variables to represent different unknown quantities

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