Class 6 Chapter 11: Basic Geometrical Concepts

Important Concepts and Formulas

1.      Lines that do not intersect each other are called parallel lines.

2.      Two distinct lines meeting at a point are called intersecting lines.

3.      Closed curves have the same starting and ending point.

4.      An angle is formed by two rays starting from a common end point.

5.      Angle AOB is written as ∠AOB. Its vertex O is always written in the middle. OA and OB are called the arms of ∠AOB or ∠BOA.

6.      A simple closed figure made up of line segments only is called a polygon.

7.      The meeting point of a pair of sides is called a vertex.

8.       Any two sides of a polygon having a common endpoint are called adjacent sides.

9.      The line segment joining two non-adjacent vertices is called a diagonal of the polygon.

10. A triangle is a polygon having least number of sides.

11. A quadrilateral has four sides, four angles and four vertices.

12. The length of the boundary of a circle is called its circumference.

13. The line segment joining any two points on the circle is called a chord.

14. Diameter is the longest chord in a circle.

15. A part of circumference (boundary) of a circle is called an arc.

16. The region in the interior of a circle enclosed by an arc and a pair of radii is called a sector.

17. The diameter divides a circle into two equal parts. Each part is called a semicircle.

18. A radius and a diameter of a circle are related to each other as follows. 
       Diameter = 2 × radius.