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Perimeter, area and volume

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Notes de leçon

Perimeter and area of 2D shapes

  • Perimeter is the distance around a shape; area is the space inside.
  • Rectangle: A = lw. Triangle: A = \frac{1}{2}bh. Parallelogram: A = bh. Trapezium: A = \frac{1}{2}(a + b)h.
  • Circle: circumference C = 2\π r = \π d; area A = \π r2.
  • For compound shapes, split into simple parts and add or subtract.
  • Use perpendicular height for triangle, parallelogram and trapezium area. Perimeter adds all outside edges; include straight edges when finding a semicircle’s perimeter.

Trapezium: perpendicular height

Trapezium: perpendicular height10 cm6 cm4 cm

Volume and surface area of 3D shapes

  • Prism: volume = cross-sectional area × length. Cuboid: V = lwh. Cylinder: V = \π r2 h; curved surface area 2\π rh.
  • Cone: V = \frac{1}{3}\π r2 h; curved surface area \π r l (slant height l).
  • Sphere: V = \frac{4}{3}\π r3; surface area 4\π r2. Pyramid: V = \frac{1}{3} \times \text{base area} \times h.
  • For a closed cylinder, add both circular ends: total surface area = 2πr² + 2πrh. A right cone has total surface area πr² + πrl, with slant height l; an open solid omits its missing faces.
  • Cylinder and cone formulas here refer to right circular solids. The h in each volume formula is perpendicular height.

Cone: radius and perpendicular height

Cone: radius and perpendicular height3 cm4 cmslant height l = √(3² + 4²) = 5 cm

Units and conversions

  • Length: cm, m. Area: cm², m². Volume: cm³, m³. 1 m² = 10 000 cm²; 1 m³ = 1 000 000 cm³; 1 litre = 1000 cm³.
  • Always state the correct units.

Perimeter and area

Perimeter and area8 cm5 cm

Strategy

  • Draw and label diagrams, identify the shape, pick the formula, and substitute carefully, giving the answer in an appropriate form (in terms of \π or to 3 s.f.).

Diapos

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Questions d'entraînement

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  1. 1.What is the area of a rectangle 5 cm by 8 cm?

    Easy
    • A13 cm²
    • B26 cm²
    • C40 cm²
    • D80 cm²
  2. 2.What is the area of a circle with radius 4 cm? Leave in terms of \π.

    Easy
    • A8\π
    • B16\π
    • C4\π
    • D64\π
  3. 3.What is the circumference of a circle with diameter 10 cm (in terms of \π)?

    Easy
    • A10\π cm
    • B20\π cm
    • C5\π cm
    • D100\π cm
  4. 4.What is the area of a parallelogram with base 7 cm and perpendicular height 4 cm?

    Easy
    • A28 cm²
    • B14 cm²
    • C22 cm²
    • D11 cm²
  5. 5.What is the area of a trapezium with parallel sides 6 cm and 10 cm and perpendicular height 4 cm?

    Easy
    • A32 cm²
    • B64 cm²
    • C24 cm²
    • D40 cm²
  6. 6.A semicircle has diameter 10 cm. What is its area in terms of \π?

    Easy
    • A12.5\π cm²
    • B25\π cm²
    • C50\π cm²
    • D5\π cm²
  7. 7.What is the volume of a cuboid 2 cm by 3 cm by 5 cm?

    Easy
    • A10 cm³
    • B30 cm³
    • C31 cm³
    • D62 cm³
  8. 8.How many cm³ are in 1 litre?

    Easy
    • A10
    • B100
    • C1000
    • D10 000

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