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What is a cube?

A cube is a three-dimensional geometric shape with six equal square faces, twelve edges, and eight vertices. Each angle between the faces is a right angle. This symmetry and equal dimensions make the cube an essential shape in geometry and architecture. It is widely used in various fields such as mathematics, physics, and computer graphics.

Formula

A cube is defined by its side length aa. From this single parameter, you can calculate several essential properties:

Surface area

The surface area of a cube is the total area covered by its six identical square faces. The formula to find the surface area is:

Surface area=6a2\text{Surface area} = 6a^2

Volume

The volume of a cube represents the amount of space enclosed within its six faces. It is given by:

Volume=a3\text{Volume} = a^3

Face diagonal

The face diagonal is the diagonal of any of the cube’s faces. The formula to find the face diagonal is based on Pythagoras’ theorem:

d=a2d = a\sqrt{2}

Cube diagonal

The cube diagonal extends from one vertex to the opposite vertex through the interior of the cube. It can be calculated using:

D=a3D = a\sqrt{3}

Examples

Example 1: Calculating cube properties

Suppose you have a cube with a side length of 4 cm. Let’s calculate its surface area, volume, face diagonal, and cube diagonal.

Surface area:

6a2=6×42=96cm26a^2 = 6 \times 4^2 = 96 \, \text{cm}^2

Volume:

a3=43=64cm3a^3 = 4^3 = 64 \, \text{cm}^3

Face diagonal:

d=425.66cmd = 4\sqrt{2} \approx 5.66 \, \text{cm}

Cube diagonal:

D=436.93cmD = 4\sqrt{3} \approx 6.93 \, \text{cm}

Example 2: Real-world application

Consider a storage cube with a side length of 1 meter. To determine the space available inside, calculate the volume:

Volume:

a3=13=1m3a^3 = 1^3 = 1 \, \text{m}^3

This measurement helps understand the capacity of the storage unit.

Interesting facts

  • Historical significance: Cubes have been part of mathematical studies since ancient civilizations, used in puzzles and architecture.
  • Rubik’s cube: An iconic 3D puzzle comprising smaller cubes, highlighting the cube’s versatility.
  • Dice: Traditional dice used in games are cubes, with numbers on each face such that the total sum of numbers on opposite faces equals seven.
  • Architecture: Cubes serve as fundamental units in modular architecture and urban planning due to their uniformity and symmetry.
  • Perfect symmetry: A cube boasts perfect symmetry across all its faces, axes, and vertices, making it a topic of interest in geometry.
  • Platonic solid: The cube is one of the five Platonic solids, characterized by its regularity and uniformity.

Frequently asked questions

How to find the volume of a cube?

To find the volume of a cube, use the formula V=a3V = a^3, where aa is the side length of the cube.

How many faces does a cube have?

A cube has six faces, each of which is a square.

What is the diagonal of a cube if the side length is 5 cm?

For a cube with side length a=5a = 5 cm, the cube diagonal dd is calculated as follows:

d=538.66cmd = 5\sqrt{3} \approx 8.66 \, \text{cm}

Why is a Rubik’s cube shaped like a cube?

The Rubik’s cube is shaped like a cube because its design allows equal distribution of smaller squares across all six faces, making it a perfect puzzle with rotational symmetry.

Can a cube be considered a rectangular prism?

Yes, a cube is a special case of a rectangular prism where all the sides are equal, making it technically a rectangular prism with square faces.

How to calculate the edge length of a cube when the volume is known?

If you know the volume VV of a cube, you can find the edge length aa by taking the cube root of the volume:

a=V3a = \sqrt[3]{V}

For a cube with a volume of 729 cm³:

a=7293=9cma = \sqrt[3]{729} = 9 \, \text{cm}