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Class 8 Area: cheat sheet
CBSE Mathematics. Areas of triangles, parallelograms, rhombuses and trapeziums, missing lengths, and areas of shapes made by joining or cutting these.
Key ideas
- The height must be perpendicular to the base it is paired with.
- A parallelogram can be cut and moved into a rectangle with the same base and height.
- A trapezium’s area uses the average of its two parallel sides.
- For a composite shape, split it into simple shapes and add, or take the cut-out parts away.
- To find a missing length, put the area and the known lengths into the formula and solve.
Remember
| Triangle | ½ × base × height |
| Parallelogram | base × height |
| Rhombus | ½ × d₁ × d₂ |
| Trapezium | ½ × (a + b) × h |
| Units | 1 m² = 10 000 cm²; 1 hectare = 10 000 m² |
Watch out
- Using a slanting side as the height.
- Forgetting the ½ for a triangle, rhombus or trapezium.
- Converting square units by 100 instead of 10 000 (m² to cm²).
Worked example
A house-shaped figure is a rectangle 19 m wide and 4 m tall with a triangle of height 8 m on top. Find its area.
Working: 19 × 4 + ½ × 19 × 8 = 76 + 76
Answer: 152 m²
Practise Area
Revise with this page, then practise: every Area sheet in the app is new, with an answer key and working.
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