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Year 7

Finding the perimeter of polygons

You can use the properties of a range of polygons to deduce their perimeters, including generalising a perimeter formula where appropriate.

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New
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Year 7

Finding the perimeter of polygons

You can use the properties of a range of polygons to deduce their perimeters, including generalising a perimeter formula where appropriate.

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Lesson details

Key learning points

  1. You can identify how to find the perimeter of polygons.
  2. The perimeter of any polygon can be found by adding but this may be time consuming.
  3. You can use a formula to find the perimeter of rectangle.
  4. You can find and use a formula to find the perimeter of any regular polygon.

Keywords

  • Polygon - A polygon is a flat (2D), closed figure made up of straight line segments.

  • Perimeter - The perimeter is the distance around a 2D shape.

Common misconception

Pupils may not count all sides when calculating the perimeter due to the complexity of the shape.

Encourage pupils to mark the sides as they record the measurement to ensure they count every side length.

Pupils may feel that one method is good enough and do not need to know alternative methods. Evaluating and critiquing their own work is a valuable skill so they should be encouraged to do this.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
Perimeter is the distance a 2D shape
Correct Answer: around
Q2.
Replacing a letter in an expression with a value is known as ______
formalisation
equalisation
subtraction
Correct answer: substitution
Q3.
If $$a$$ = 10 and $$b$$ = 7, what is the value of the expression 2$$b$$ + 2$$a$$?
Correct Answer: 34, Thirty four, thirty-four, thirty four
Q4.
Substitute the value $$y$$ = 2 into the expression 3$$y$$ $$+$$ 5 and evaluate the result
Correct Answer: 11, eleven, Eleven
Q5.
Izzy wants to add these values: 0.24, 0.5 and 17.3 together using column addition. Select the correct layout.
An image in a quiz
Values right aligned
Values left aligned
Values centered
Correct answer: Values aligned by the decimal point
Q6.
Evaluate 18.41 $$+$$ 16.7
3.448
3.511
34.48
Correct answer: 35.11

Exit quiz

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6 Questions

Q1.
Perimeter is the distance around a 2D shape. It can be calculated by all of the edges together.
Correct Answer: summing, adding
Q2.
True or false? Number bonds can be used to calculate the perimeter more efficiently.
Correct answer: True
False
Q3.
Which of these formulas could not be used to calculate the perimeter ($$P$$) of this square?
An image in a quiz
$$P = 4b$$
$$P = 2b + 2b$$
$$P = 3b + b$$
Correct answer: $$P = b + b + b + b + b$$
Q4.
Complete the formula for the perimeter of this trapezium. $$P = $$
An image in a quiz
Correct Answer: a + b + 2d, a + b + d + d
Q5.
You can write a to calculate the perimeter in an efficient way.
Correct Answer: formula
Q6.
What is the mathematical name for the polygon whose perimeter ($$P$$) can be calculated using the formula $$P = t + r + 2w + y$$?
triangle
quadrilateral
Correct answer: pentagon
hexagon