CBSE Class 8 Math, Understanding Quadrilaterals

Key Notes
Understanding Quadrilaterals
Polygon – Polygon is a combination of two Greek words Polus + Gonia, in which Polus means many and Gonia means Corner or angle.
Classification of Polygons
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
A triangle has three sides,
Thus, Angle sum of a triangle = (3 – 2) × 180° = 1 × 180° = 180°