Exercise 7.2 deals with the condition where three lines meet to create angles. In this exercise you will learn to figure out unknown angles using basic facts, such as the sum of angles on a straight line or vertically opposite angles. It is an important foundation in geometry and is useful to enhance your questioning skills.
This exercise is based on the recent NCERT syllabus and aims to teach you angles clearly and usefully through examples and step-by-step questions. Working through these questions should not only prepare you for internal examinations but also develop your reasoning ability.
For clear and accurate answers to each question, refer to the NCERT Solutions prepared in a simple and easy-to-follow style that will correspond to your level of learning.
The free PDF of the NCERT Solutions for Class 7 Maths Chapter 7 exercise 7.2 is available for download from below:
Exercise 7.2 helps you understand how to work with angles formed when three lines cross each other. Below are the key concepts covered in this exercise:
1. We checked by construction that there are no triangles having side lengths 3 cm,4 cm and 8 cm;2 cm,3 cm and 6 cm . Check if you could have found this without trying to construct the triangle.
Sol. Yes, without constructing the triangles, we could have determined that they cannot exist using the triangle inequality.
i.e. 3+4<8
and 2+3<6
Hence, both the triangles cannot be formed.
2. Can we say anything about the existence of a triangle for each of the following sets of lengths?
(i) 10 km,10 km and 25 km
(ii) 5 mm,10 mm and 20 mm
(iii) 12 cm,20 cm and 40 cm
Sol. We know that the sum of the lengths of any two sides of a triangle must be greater than the length of the third side.
(i) Here, 10+10<25
So, a triangle cannot be formed.
(ii) Here, 5+10<20
So, a triangle cannot be formed.
(iii) Here, 12+20<40
So, a triangle cannot be formed.
(Session 2026 - 27)