# Basic Geometrical Concepts

Here we will recall about the basic geometrical concepts.

Basic Geometrical Concepts:

Axiom: It is a proposition that is not proved but considered to be self-evident or subject to necessary decision. Its truth is taken for granted and serves as a starting point for deducing and concluding other truths.

For Example:

Whole is greater than the part.

Things that are equal to same thing are equal to one another.

Statement: It is a question that is definitely true or definitely false.

For Example:

Every triangle has three sides. This statement is true.

No prime number is even. This statement is false.

Theorem: A formula that is provable without any further assumption is called a theorem. A theorem can be deduced from previously accepted statements such as axiom.

For Example:

In a right angled triangle, the sum of the squares of two sides is equal to the square of the longest side.

Corollary: Result that is trivial or self-evident from a theorem is known as a corollary. Corollary is simply something which we can prove from some other theorem.

For Example:

Theorem: The sum of interior angles of a triangle is 180°.

Its corollary: The sum of interior angles of a quadrilateral is 360°.

Lines and Angles

Fundamental Geometrical Concepts

Angles

Classification of Angles

Related Angles

Some Geometric Terms and Results

Complementary Angles

Supplementary Angles

Complementary and Supplementary Angles

Linear Pair of Angles

Vertically Opposite Angles

Parallel Lines

Transversal Line

Parallel and Transversal Lines