Year 7 - Maths
Calculating missing lengths with perimeter of polygons
Perimeter and area
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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 pupils investigate how to calculate the area and perimeter of rectilinear shapes, and composite shapes using rectangles and triangles. They will also derive simple area formulae.
Lesson Summary
You will learn to use the properties of a range of polygons and the perimeter of a given polygon to deduce missing side lengths.
Key Notes
- Missing side lengths can be found if the perimeter is known.
- Perimeter problems involve a context where the distance around a 2D shape is wanted.
Vocabulary To Learn
- Perimeter: The perimeter is the distance around a 2D shape.
- Polygon: A polygon is a flat (2D), closed figure made up of straight line segments.
Common Mistakes To Avoid
- Pupils may struggle to think of a different context to apply to finding the perimeter.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
Missing side lengths can be found if the perimeter is known. Perimeter problems involve a context where the distance around a 2D shape is wanted.
2. Use this key word in a maths sentence and explain it clearly. 'Perimeter'
The perimeter is the distance around a 2D shape. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Pupils may struggle to think of a different context to apply to finding the perimeter. Correction: An alternative context could be: putting a ribbon around a cake and leaving space for decoration.
More Lessons In This Unit
- Area of a trapezium Study Guide
- Area of a triangle Study Guide
- Area of composite rectilinear shapes Study Guide
- Calculating missing side lengths from the area of a trapezium Study Guide
- Calculating missing side lengths from the area of composite rectilinear shapes Study Guide
- Checking understanding of perimeter and area Study Guide
- Finding the perimeter of polygons Study Guide
- Perimeter with composite rectilinear shapes Study Guide
- Problem solving with perimeter and area Study Guide
- Securing understanding of perimeter and area Study Guide
- Using the formula for the area of a triangle Study Guide
Browse all guides in the Year 7 Maths guide library.