Knowledge Organiser: Area of Rectangles & Triangles
Part of Area of Rectangles & Triangles · GCSE GCSE Mathematics revision
This topic summary covers Knowledge Organiser: Area of Rectangles & Triangles within Area of Rectangles & Triangles for GCSE Mathematics. Revise Area of Rectangles & Triangles in Geometry & Measures for GCSE Mathematics with 12 exam-style questions and 6 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 8 of 8 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 8 of 8
Practice
12 questions
Recall
6 flashcards
Knowledge Organiser: Area of Rectangles & Triangles
Key Terms
- Area: The amount of space a shape covers, measured in square units
- Perpendicular height: The height at 90° to the base — NOT the slant side
- Base: The bottom side of a shape used in area calculations
- Composite shape: A shape made from two or more simpler shapes
Must-Know Facts
- Area is always in square units: cm², m², mm²
- Triangle area = ½ × rectangle area with same base and height
- Height MUST be perpendicular (90°) to the base
- For composite shapes: split into simpler parts, find each area, then add or subtract
- To find a missing side: rearrange the formula (e.g. l = Area ÷ w)
Key Formulas
- Rectangle: A = l × w
- Square: A = s²
- Triangle: A = ½ × b × h
- Missing side: side = Area ÷ other side
Common Mistakes
- Forgetting the ½ in triangle area: A = ½ × base × height — the ½ is always required
- Height must be perpendicular: The height is the perpendicular distance to the base, not the slant side
- Units: Area is always cm², m², etc. — never just cm or m
- Composite shapes: Split into rectangles and triangles, calculate each area separately, then add or subtract
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Practice Questions for Area of Rectangles & Triangles
Which formula gives the area of a rectangle with length l and width w?
Explain why the area formula for a triangle uses the perpendicular height rather than the slant height.
Quick Recall Flashcards
12 questions on Area of Rectangles & Triangles — practise free
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