NCERT Book Class 7 Maths Chapter 6 The Triangle and its Properties

88 MATHEMATICS

Chapter 6
The Triangle and
its Properties

6.1 I NTRODUCTION
A triangle, you have seen, is a simple closed curve made of three line
segments. It has three vertices, three sides and three angles.
Here is ∆ABC (Fig 6.1). It has
Sides: AB , BC , CA
Angles: ∠BAC, ∠ABC, ∠BCA
Fig 6.1
Vertices: A, B, C
The side opposite to the vertex A is BC. Can you name the angle opposite to the side AB?
You know how to classify triangles based on the (i) sides (ii) angles.
(i) Based on Sides: Scalene, Isosceles and Equilateral triangles.
(ii) Based on Angles: Acute-angled, Obtuse-angled and Right-angled triangles.
Make paper-cut models of the above triangular shapes. Compare your models with
those of your friends and discuss about them.

TRY THESE
1. Write the six elements (i.e., the 3 sides and the 3 angles) of ∆ABC.
2. Write the:
(i) Side opposite to the vertex Q of ∆PQR
(ii) Angle opposite to the side LM of ∆LMN
(iii) Vertex opposite to the side RT of ∆RST
3. Look at Fig 6.2 and classify each of the triangles according to its
(a) Sides
(b) Angles