4.10.5

Surface Area of Composite Solids

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Surface Area of Composite Solids

What is a composite solid?

What is a composite solid?

  • A composite solid is made by joining two or more simple 3D shapes together.

  • To find the total surface area, we only calculate the area of the faces on the outside.

The Hidden Face Rule

The Hidden Face Rule

  • When two shapes are glued together, their touching faces become hidden inside.

  • These hidden faces do not count towards the total surface area.

  • Remember to subtract the overlapping area from your final calculation.

Cylinder on a Cuboid

Cylinder on a Cuboid

  • Imagine a circular cylinder standing on a rectangular box.

  • The top of the box is not a full rectangle anymore; it has a circular footprint covering it.

  • Calculate the full box, full cylinder, and subtract the circular base 2 times (once from each shape).

Hollow Solids

Hollow Solids

  • If a composite shape has a hole drilled through it, the total surface area changes.

  • You must subtract the shape of the hole from the outside faces.

  • But you must add the new surface area of the inside walls.

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1

Number

1.1

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1.2

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1.4

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1.5

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1.6

Structure of Calculations

1.7

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Percentage Change

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Using Numbers

2

Algebra

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3

Ratio

4

Geometry

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Area & Perimeter

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Properties of Shapes

4.3

Angles

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Trigonometry

4.5

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4.6

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4.7

Circle Theorems

4.8

Pythagoras

4.9

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4.10

Surface Area

4.11

Volume

4.12

Vectors

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Transformations

4.14

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4.15

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4.17

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4.18

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4.19

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3D Shapes

5

Probability

6

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