Introduction to Geometry

Understanding Geometry

branch of mathematics regarding geometric figures and properties of space

Branch of mathematics regarding geometric figures and properties of space.

Geometry is a branch of mathematics that deals with the properties, measurement, and relationships of points, lines, angles, surfaces, and solids. It is a practical science that is applied in numerous fields such as architecture, engineering, astronomy, and art. This unit will provide a comprehensive understanding of the basic elements of geometry.

Basic Elements of Geometry


A point in geometry is a location. It has no size, only position. It is usually represented by a dot and named by a capital letter.


A line is a straight one-dimensional figure that extends infinitely in both directions. It is defined by two points within it. There are different types of lines:

  • Straight Line: A line that lies evenly with the points on itself.
  • Ray: A line with a start point but no end point (it goes to infinity).
  • Line Segment: A part of a line that is bounded by two distinct end points.


A plane in geometry is a flat, two-dimensional surface that extends infinitely far. A plane is defined by three points not in a straight line.

Types of Lines

There are several types of lines in geometry:

  • Parallel Lines: Two lines that are always the same distance apart and never touch.
  • Perpendicular Lines: Two lines that intersect at a right angle.
  • Intersecting Lines: Two lines that cross at a point.


An angle measures the amount of turn between two lines that meet at a point. There are four main types of angles:

  • Acute Angle: An angle less than 90 degrees.
  • Right Angle: An angle of exactly 90 degrees.
  • Obtuse Angle: An angle greater than 90 degrees but less than 180 degrees.
  • Straight Angle: An angle of 180 degrees.

Understanding Dimensions

In geometry, dimensions refer to the measurable extents of a figure. There are three dimensions in geometry:

  • One-Dimensional: This includes only length (e.g., a line).
  • Two-Dimensional: This includes length and width (e.g., a rectangle).
  • Three-Dimensional: This includes length, width, and height (e.g., a cube).

In conclusion, understanding these basic elements of geometry is crucial as they form the foundation for more complex geometric concepts. The next units will delve deeper into geometric shapes and their properties, with a particular focus on triangles, which are essential for understanding the Pythagorean theorem.