## Chapter 7 Triangles

Chapter 7.TrianglesDefinition:- a closed figure formed by three intersecting lines is called a triangle. (‘Tri’ means ‘three’). A triangle has three sides, three angles and three vertices. For example, in triangle ABC, denoted as ABC ; AB, BC, CA are the three sides, <A, <B, <C are the three angles and A, B, C are … Read more

## Chapter 5. INTRODUCTION TO EUCLID’S GEOMETRY

1. The word ‘geometry’ comes form the Greek words ‘geo’, meaning the ‘earth’, and ‘metrein’, meaning ‘to measure’. Geometry appears to have originated from the need for measuring land. 2. Theorem 5.1 : Two distinct lines cannot have more than one point in common. Proof : Here we are given two lines l and m. … Read more

## Chapter 3.Coordinate Geometry

Important Points to Remember 1. What are the coordinates of the origin O? It has zero distance from both the axes so that its abscissa and ordinate are both zero. Therefore, the coordinates of the origin are (0, 0). 2. the axes (plural of the word‘axis’) divide the plane into four parts. These four parts … Read more

## 1.Number System

Class IX(Chapter 1.Numbers System) 1.Natural Number (N) : All number s  used in counting are known as natural numbers such  as 1,2,3,….., is called natural number.Denoted by N.N={1,2,3,……,n}. 2.Whole Number(W): All natural numbers including zero , is called Whole numbers.Denoted by W. W={0,1,2,3,…..n}. 3.Integers(I):- All number with +ve and –ve sign including 0, is known … Read more