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Sunday, 10 June 2012

Angles And Triangles : Basic Geometry- Part- I

In geometry, an angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle.

Picture of an Angle

Angle is also used to designate the measure of an angle or of a rotation. This measure is the ratio of the length of a circular arc by its radius. In the case of an angle (figure), the arc is centered at the vertex and delimited by the sides. In the case of a rotation, the arc is centered at the center of the rotation and delimited by any point and its image by the rotation.

In geometry, a protractor is a square, circular or semicircular tool, typically in transparent perspex, for measuring angles. The units of measurement utilized are usually degrees (°).

Picture of Protractor

They are used for a variety of mechanical and engineering-related applications, but perhaps the most common use is in geometry lessons in schools.

Drawing a Angle with Protector and Pencil:

                                                                                 Animation Showing Draw a Angle with Protector and Pencil.
Draw a line Base Ray of  an Angle

Draw other Ray of an Angle

Draw an Angle

Different Types of Angles:

Acute Angle
Acute Angle:                                                         
Angle which is smaller than right angle or 90 degrees   known as acute angle Example: angles from 1 degrees to 89 degrees

Right Angle

Right Angle:                                    
Angle which is equal to 90 degrees known as right angle Example: angles from 90 degrees.

Obtuse Angle

Obtuse Angle:                                                                                                                                     
Angle which is greater than 90 degrees but smaller than 180 degrees known as obtuse angle Example: angles from 91degrees to 179 degrees

Straight Angle

Straight Angle:                                        
Angle which is equal to 180 degrees known as straight angle Example: angle of 180 degrees

Reflex Angle
Reflex Angle: 
Angle which is greater than 180 degrees but smaller than 360 degrees ,known as reflex angle Example: angle from 180 degrees to 359 degrees

Complete Angle

Complete Angle:                                                                                                                                                                            
Angle which is equal to 360 degrees ,known as complete angle Example: angle of 360 degrees .

                                                                                Animation Showing Drawing Different types of Angles
A triangle is one of the basic shapes of geometry: a polygon with three corners or vertices and three sides or edges which are line segments. A triangle with vertices A, B, and C is denoted \triangle ABC.

Picture of Triangle

Division of Triangle on the basis of length of Sides

Equilateral Triangle

1) Equilateral Triangle
Triangle having  all three sides are equal in length.  

Isosceles Triangle

2) Isoscales Triangle
Triangle having  only two sides are equal in length.

Scalene Triangle

 3)Scalene Triangle
Triangle having  all sides are unequal in length.  

                                                                             Animation showing Division of different Triangle on the basis of length of Sides

Division of Triangle on the basis of Angle of Sides

Acute Angle Triangle

1) Acute Angle Triangle
Triangle having  angles of all three side  are acute (less than 90 degrees) .

Obtuse Angle Triangle

2) Obtuse Angle Triangle
Triangle having  angle of one side  is obtuse angle ( more than 90 degrees) .

Right Angle Triangle

3) Right Angle Triangle
Triangle having  angles of one side  is right angle ( 90 degrees) .

                                                                                     Animation showing Division of different Triangle on the basis of different Angles.


  1. I think at the time math is very difficult subject, parents should help kids in solving math problems. and about 12 sided I want to share a simple definition as-12 sided polygon is called as dodecagon, This is one type of regular polygons, it may be regular or irregular. It’s a 12 sided closed figure.



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