WELCOME

NAME OF THE TEACHER : ANEES A J

STANDARD:9

UNIT :POLYGONS

TOPIC : INTERIOR ANGLES OF POLYGON

OBJECTIVE : TO UNDERSTAND THAT THE SUM OF INTERIOR ANGLES

A POLYGON HAVING ‘N’ SIDES =(N-2)*180

INTERIOR ANGLES OF A POLYGON

STEPS TO FIND OUT THE INTERIOR ANGLES OF POLYGONS

Polygons can be divided into triangles by joining alternative vertices.

The number of triangle = Two less than the number of sides of the original polygon.

Since the sum of the angles of a triangle is 180, we can find the sum of angles of polygon by multiplying the number of triangles with 180

SUM OF INTERIOR ANGLES

TRIANGLE QUADRILATERAL= PENTAGON=

2 TRIANGLES 3 TRIANGLES

HEXAGON= 4 TRIANGLES HEPTAGON= 5 TRIANGLES

SHAPE NUMBER OF SIDES

NUMBER OF TRIANGLES

SUM OF THE ANGLES (DEGREE)

TRIANGLE 3 1=(3-2) 1*180=180

QUADRILATERAL

4 2=(4-2)

2*180=360

PENTAGON

5 3=(5-2) 3*180=540

HEXAGON

6 4=(6-2)

4*180=720

From the above table we can conclude that the sum of the angles of a polygon having ‘n’ sides is (n-2)180. As the number of sides increases the sum of angles increases by 180 degree.

THANK YOU