Parallel lines


Hello, my name is Benjawan Rangphet P. 5/3 No. 11

Today I will talk about parallel lines,interior angles and external angles.

parallel lines


ผลการค้นหารูปภาพสำหรับ parallel lines





are lines in a plane which do not meet; that is, two lines in a plane that do not intersect or touch each other at any point are said to be parallel. By extension, a line and a plane, or two planes, in three-dimensional Euclidean space that do not share a point are said to be parallel. However, two lines in three-dimensional space which do not meet must be in a common plane to be considered parallel; otherwise they are called skew lines. Parallel planes are planes in the same three-dimensional space that never meet.

Parallel lines are the subject of Euclid‘s parallel postulate.[1] Parallelism is primarily a property of affine geometries and Euclidean geometry is a special instance of this type of geometry. In some other geometries, such as hyperbolic geometry, lines can have analogous properties that are referred to as parallelism.

interior angles

ผลการค้นหารูปภาพสำหรับ interior angles


Interior angle” redirects here. For interior angles on the same side of the transversal, see Transversal line.

In geometry, an angle of a polygon is formed by two sides of the polygon that share an endpoint. For a simple (non-self-intersecting) polygon, regardless of whether it is convex or non-convex, this angle is called an interior angle (or internal angle) if a point within the angle is in the interior of the polygon. A polygon has exactly one internal angle per vertex.

If every internal angle of a simple polygon is less than 180°, the polygon is called convex.

In contrast, an exterior angle (or external angle) is an angle formed by one side of a simple polygon and a line extended from an adjacent side.


external angles.


The exterior angle theorem is Proposition 1.16 in Euclid’s Elements, which states that the measure of an exterior angle of a triangle is greater than either of the measures of the remote interior angles. This is a fundamental result in absolute geometry because its proof does not depend upon the parallel postulate.

In several high school treatments of geometry, the term “exterior angle theorem” has been applied to a different result,[1] namely the portion of Proposition 1.32 which states that the measure of an exterior angle of a triangle is equal to the sum of the measures of the remote interior angles. This result, which depends upon Euclid’s parallel postulate will be referred to as the “High school exterior angle theorem” (HSEAT) to distinguish it from Euclid’s exterior angle theorem.

Some authors refer to the “High school exterior angle theorem” as the strong form of the exterior angle theorem and “Euclid’s exterior angle theorem” as the weak form.