CBSE Class 8 Math, Understanding Quadrilaterals

Polygon – Polygon is a combination of two Greek words Polus + Gonia, in which Polus means many and Gonia means Corner or angle.

Polygons are classified as per their sides or vertices they have.

(a) Triangle – A triangle has three sides and three vertices. A triangle is of three types: Equilateral, Isosceles and Scalene.

b) Quadrilateral – A quadrilateral has four sides and consecutively four vertices.

(c) Pentagon – (Penta stands for five) A pentagon has five sides and five vertices.

(d) Hexagon – (Hexa stands for six) A hexagon has six sides and six vertices.

(e) Heptagon – (Hepta stands for seven) A heptagon has seven sides and seven vertices.

(f) Octagon – (Octa stands for eight) an octagon has eight sides and eight vertices.

(g) Nonagon – (Nona stands for nine) A nonagon has nine sides and nine vertices.

(h) Decagon – (Deca stands for ten) A decagon has ten sides and ten vertices.

A line segments which connects two non-consecutive vertices of a polygon is called diagonal.

               

This is the combination of two Latin words; Quardi + Latus. Quadri . means four and Latus means side.

So, a polygon that has four sides is known as a quadrilateral. In a quadrilateral, sides are straight lines and are two dimensional. Square, rectangle, rhombus, parallelogram, etc. are the examples of quadrilateral.

Formula for angle sum of a polygon = (n – 2) × 180°.

Where ‘n’ is the number of sides

Example:

A triangle has three sides,

Thus, Angle sum of a triangle = (3 – 2) × 180° = 1 × 180° = 180°