## Fundamental Concepts of Euclidean Geometry

In uncovering the secrets of the fundamentals of geometry, Euclid realised that first must come the very basic fundamental concepts. Certain questions had to be answered to define these fundamental constituents of the field, such as *what is a point, *or *what is a line?*

### Points

Euclid defined a point in the following way: “a point is that which has no part." In essence, this simply means that a point is just a location in space that has no dimensions. That is to say, though it has spatial parameters to define its location, **it does not actually occupy any space itself**.

### Lines

Euclid also defined something called a **line**. This he defined as "a length without a breadth." In essence, just a 1-dimensional segment with a finite length. He posited that a line could be extended infinitely in either direction. This is an area where modern geometry differs from Euclid's fundamentals, as now we refer to an infinitely extended line simply as a **line** and Euclid's line of finite length as a **line segment**. This is an important distinction to remember for the sake of correctness. Let's take a look at the difference below. Euclid also defined something called a *ray*, which similar to a line is infinitely long, however, it has a defined starting point. It is also sometimes known as a *half-line.*

A line is a straight, 1-dimensional figure that extends indefinitely in both directions. A line segment is a straight, 1-dimensional figure of finite length that connects two points. A ray is a straight one-dimensional figure that extends infinitely in one direction, from a defined starting point.

### Planes

A plane, in many ways, can be considered as similar to a line, but in two dimensions. A plane is simply a surface that extends indefinitely. A plane can exist in 2-dimensional spaces as well as 3-dimensional spaces and higher.

A plane is a 2-dimensional figure that extends indefinitely in four directions.

### Angles

Angles were defined by Euclid as "the inclination of two straight lines." This essentially can be described in simpler terms as the rotational distance between two lines or line segments that share a point, i.e how much would we have to rotate one line before it lines up with the other. The shared point is known as the **vertex **of the angle.

An angle is a measure of rotational space between two lines or line segments.

### Dimensions

Dimensions are an important aspect of the fundamentals of geometry, which specifically deals with **spatial dimensions**. Spatial dimensions in mathematics and physics can be defined as the minimum number of coordinates required to describe a point in that space. For instance, a line has 1-dimensions as only a single number is required to specify a point on that line. Equally, if you wanted to specify a point on an x-y axis you would need two coordinates an x and y coordinate and on a set of 3-dimensional axes, you would need a third coordinate - the z coordinate.

Dimensions are extensions of space in a single direction, the length along which can be used to describe the location of a point in that dimension. Multiple dimensions can be combined to describe geometric properties with increasing complexity.

### Area

Area is a measurement that describes the size of a certain 2-dimensional region. There are various formulas that can be used in calculating the area of certain shapes. A good way to visualise area is to divide up a 2-dimensional space into squares. The area of the shape is simply equal to the number of squares contained inside it.

Area is a measurement that describes the size of a certain 2-dimensional region of space.

### Volume

Much like area, volume is a measure that quantifies the size of a certain region of space. Volume, however, quantifies the size of a region in **3-dimensional **space. All 3-dimensional shapes have volume, and similar to area there are many useful formulas for calculating the volumes of various shapes. We can visualise volume in much the same way as area, but rather than using small squares, we count the number of small cubes inside a shape. The image below depicts a cube in 3-dimensional space. How much space does the cube take up? Well, by counting we can see that the cube takes up the space of 64 smaller cubes, each with a volume of 1 units^{3}.

Volume is a measurement that describes the size of a certain 3-dimensional region of space.

A cube in 3-dimensional space, John Hannah - StudySmarter Originals

### Units

An important part of the fundamentals of geometry is the use of various units. In geometry, we use two basic types of units: units of **length** and units of **angles****.**

A unit is a convention that helps us define how large something is. For instance, a unit of **length** can help us define how long something is, and a unit of volume can help us define how large a 3-dimensional shape is.

**Units of Length**

There are two primary systems for units of length. These systems are the **metric **and **imperial **systems. The metric system deals in units of centimetres, metres, kilometres etc. whereas the imperial system works in units inches, feet, yards, miles etc.

Length is a 1-dimensional unit, however, units of 2-dimensions (area) and 3-dimensions (volume) exist which are composed of these units of length. The convention for the naming of these dimensions is shown in the table below.

Length | Area | Volume |

$cm$$cm$ | $c{m}^{2}$ | $c{m}^{3}$ |

$m$ | ${m}^{2}$ | ${m}^{3}$ |

$km$$km$ | $k{m}^{2}$ | $k{m}^{3}$ |

**Units of Angles**

Degrees and radians are the two main units for the measurement of angles and it's very easy to run into problems if the distinction between the two isn't clear!

Firstly, it is important to recognise that degrees are an arbitrary unit of measurement that simply arose from the fact of the Earth's rotation. Ancient people watching the constellations in the sky move on a yearly cycle figured that since there were 360 days in a year (there are really 365 but they got pretty close!) that there should be 360 degrees in a full rotation. This has proved a simple and intuitive way to discuss angles as human beings, after all, we aren't computers and sometimes closely packed decimal numbers can be confusing.

However, since these early scholars sat looking at the stars, we have discovered another, arguably more mathematically sound way of describing angles. This unit is known as the **radian**.

Radians, rather than being related simply to 'amount of rotation', are related to distance travelled around an arc. Really, radians are in fact **the distance travelled around an arc divided by the distance to the pivot point of that arc**. If we take the equation relating a circle's circumference to its radius, we can find how many radians in a full rotation of 360^{o}.

$C=2\mathrm{\pi r}$

$\frac{C}{r}=2\mathrm{\pi}$

So in 360^{o} there are $2\mathrm{\pi}$ radians. From this, we can see that

Degrees | Radians |

360^{o} | $2\mathrm{\pi}$ |

180^{o} | $\mathrm{\pi}$ |

90^{o} | $\frac{\mathrm{\pi}}{2}$ |

45^{o} | $\frac{\mathrm{\pi}}{4}$ |

It is important when using a calculator if it is set to treat your angles as **radians **or **degrees** when dealing with trigonometric functions to obtain the correct answer. Technically all mathematical functions taking angles as inputs work in radians.

## The Fundamental Principles of Euclidean Geometry

Euclid made five fundamental postulates when delving into the field of geometry. These postulates were fundamental principles of geometry that he held to be self-evident, and informed all further principles and concepts of geometry thereafter.

Postulates of Euclidean Geometry |

1. A straight line segment can be drawn joining any two points. |

2. Any straight line segment can be extended indefinitely in a straight line. |

3. Given any straight line segment, a circle can be drawn having the segment as radius and one endpoint as centre. |

4. All right angles are congruent. |

5. Given a line and a point not on that line, there exist an infinite number of lines through the given point parallel to the given line. |

## Fundamentals of Geometry - Key takeaways

- Many of the fundamentals of geometry that are used today were popularised by a Greek mathematician known as Euclid.
- A point is a single location space that has no size.
- A line is a 1-dimensional figure that extends indefinitely.
- A line segment is a 1-dimensional figure with finite start and end-points.
- A plane is a 2-dimensional figure that extends indefinitely.
- Angles are a measure of rotational distance.
- Dimensions can be described as the coordinates required to define a point in a certain space.
- Area is a measure of the 2-dimensional size of a shape.
- Volume is the measure of the 3-dimensional size of a shape.
- Units are a convention used to define the size of various quantities.
- Units of length are either of the imperial system or the metric system.
- Units of angles are either radians or degrees.
- Euclid defined five postulates of geometry that he held as self-evident truths.

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##### Frequently Asked Questions about Fundamentals of Geometry

What are the fundamentals of geometry?

The fundamentals of geometry are a set of rules and definitions upon which all other areas of geometry are built.

What are the most basic fundamental components of geometry?

The most basic, fundamental components of geometry are points, lines, and planes.

What are dimensions?

Dimensions are an extension of space in a single direction, the length along which can be used to describe the location of a point in that dimension. To make things simpler, we can think of the number of dimensions in a space to be the number of coordinates required to fully describe the location of a point in that space.

What is the fundamental theorem of similarity geometry?

The fundamental theorem of similarity states that *a line segment splits two sides of a triangle into proportional segments if and only if the segment is parallel to the triangle's third side.*

What are the fundamentals of descriptive geometry?

Geometry can be described largely in terms of points, lines, planes, line segments, dimensions, and angles.

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