# Geometry Postulates

Euclidean geometry is the study of shapes of flat surfaces. Shapes that do not fall under this category are referred to as non-Euclidean geometry.

The foundation of Euclidean geometry is a set of five postulates. These are also known as axioms. They are statements that do not need to be proven and from which other lemmas and theorems can be derived.

## Lines

The concept of line is an important one in geometry. It is defined as a 1-D figure that can be extended to infinity in opposite directions. It has a variety of properties that are useful in geometry problems. The most basic property of a line is that its supplementary angle (angle formed between two adjacent lines) is 180 degrees.

The line can also be described in terms of its slope or gradient. The equation of a line is given by y = m(x-x) + y. Lines are very important in geometry, and they can be found everywhere in our daily lives. They can be used to represent paths of rays of light, for example.

It is essential to understand the relationships between the “undefined” terms of a point, a line and a plane in order to strengthen and expand your knowledge of geometry. Using Brighterly’s selection of geometry worksheets can help you do just that.

## Circles

Circles are familiar shapes that can be found in a number of everyday objects such as a wheel, dining plate or coin. Circles are unique among other shapes in that all points lie at the same distance from the centre.

There are many properties that can be proved about circles. For example, circles with equal radii are congruent and circles with different radii appear similar. Also, a line segment joining two intersection points of two circles is perpendicular to the line connecting their centers.

Another property of circles is the length of a circle’s circumference, which is twice pi times radius squared. Another property is that the central angle subtended by a chord at the center of the circle is double the angle subtended by the same chord at any other point on the circumference of the circle. There are several other interesting facts about circles. These are called circle properties and can be proved using various geometric tools such as compass and ruler.

## Angles

An angle is a figure formed by two rays that share a common endpoint. It is usually measured in degrees, which are represented by the symbol °. It can be classified as positive, negative or reflex (acute, obtuse or straight).

When two angles have the same measure, they are said to be congruent. This means that their sines, cosines and tangents are all equal. Two angles that have opposite measures are called complementary. The sum of their sines is 180°, and the sum of their cosines and tangents is 360°.

An angle can also be described by the letters that are used to name it: alpha, beta and theta. The letter that is placed in the middle of the shape is known as its vertex, or corner point. The other two sides of the angle are referred to as its arms. The initial side is known as the base of the angle, and the terminal side is the apex of the angle.

## Planes

A plane is a flat two-dimensional surface that extends indefinitely in all directions. It has infinite length and width, and zero thickness. It is usually represented by a square with four sides, and is named with a single capital letter. A plane can be defined by any three non-collinear points, and it is possible to have parallel or intersecting planes.

A vector that is perpendicular to a plane is called a normal to that plane. It can be described by its origin, an ordered pair of perpendicular lines (or axes) from which it is measured, and its magnitude and direction.

Geometry studies the properties of plane figures, including lines, line segments, polygons, circles and more. Plane geometry is a subset of the larger discipline known as solid geometry. The axioms and postulates of plane geometry are very similar to those of three-dimensional space, but there are some important differences. For example, a circle in a plane has constant radius, while a circle in three-dimensional space can have varying radius.