Year 4 - Maths
Know that a regular polygon has sides that are the same length and angles that are the same size
Perimeter
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
In this unit pupil will learn perimeter as the distance around the edge of a 2D shape. They will learn perimeter is measured in units of length found by counting units and by calculating by adding the side lengths of a 2D shape.
Lesson Summary
You know that a regular polygon has sides that are the same length and angles that are the same size.
Key Notes
- In a regular polygon, the sides are all the same length and the angles are all the same size
- In an irregular polygon the sides and angles are not all the same sizes
- Irregular polygons can have some angles and sides the same sizes
Vocabulary To Learn
- Regular polygon: A polygon where all angles are equal and all side lengths are equal.
- Irregular polygon: A polygon where not all angles are equal and / or not all side lengths are equal.
- Interior angles: Interior angles are the angles formed inside a polygon by two of its sides.
Common Mistakes To Avoid
- Many polygons appear regular as all of the sides are the same length. However, it is possible (as the lesson shows) to have polygons which are the same length sides but different interior angles.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
In a regular polygon, the sides are all the same length and the angles are all the same size. In an irregular polygon the sides and angles are not all the same sizes.
2. Use this key word in a maths sentence and explain it clearly. 'Regular polygon'
A polygon where all angles are equal and all side lengths are equal. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Many polygons appear regular as all of the sides are the same length. However, it is possible (as the lesson shows) to have polygons which are the same length sides but different interior angles. Correction: Pupils should have previous experience of right angles. Use a right angle 'measurer' to prove that some of the angles in a shape are greater than a right angle and some smaller; as the angles are not all equal, it is not a regular polygon.
More Lessons In This Unit
- Calculate the side length of a regular polygon by division where the perimeter is known Study Guide
- Know that perimeter can be calculated by adding together the side lengths of a 2D shape Study Guide
- Know that perimeter is measured in units of length and can be found by counting or measuring units Study Guide
- Know that the perimeter is the distance around a 2D shape Study Guide
- Know that the perimeter of a rectangle can be calculated by addition and multiplication Study Guide
- Know that unknown side lengths can be calculated from the perimeter and known side lengths Study Guide
- Solve problems involving the perimeter and side lengths of polygons Study Guide
- Understand that different shapes can have the same perimeter Study Guide
- Understand that the perimeter of a regular polygon can be calculated by multiplication Study Guide
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