Constructions Class 9 Notes: Chapter 11

Class 9 CBSE math notes are provided here to help students overcome the challenges in learning the concepts of constructions. The notes which contain detailed information can be used as a great reference tool for studying productively as well as completing revisions before the exams. Some of the topics that are covered in the construction chapter are;

  • Definition of Construction.
  • Carrying out some basic constructions and giving reasons as to why these constructions are valid.
  • Constructions of a triangle.
  • Practice Questions.

What is Construction?

The construction which is an important part of geometry basically means drawing angles, shapes, and lines in perfection. Constructions are usually carried out using only a ruler, compass and a pencil. As such, in chapter 11 students learn about the steps of drawing the perfect geometrical figures.

Basic Constructions

Construction 1: To construct a given angle.

Constructions Class 9 Notes

Construction 2: To construct the bisector of a given angle.

Constructions Class 9 Notes
Constructions Class 9 Notes

Construction 3: To construct the perpendicular bisector of a given line segment.

Steps of Construction

Constructions Class 9 Notes

Construction 4: To construct an angle of 60 degrees.

Constructions Class 9 Notes
Constructions Class 9 Notes

Construction of Triangles

When we talk about the construction of a triangle we usually do not need the dimension and angles. However, there are some key conditions that can be followed when creating a triangle. Some of the conditions are as follows;

Constructions Class 9 Notes

Important Questions:

  • Construct an angle of 90 degrees and justify the construction.
  • Construct a triangle PQR in which QR = 5cm, ∠Q = 60° and PR – PQ = 2cm.
  • Construct a right triangle whose base is 10cm and the sum of its hypotenuse and another side is 15 cm.

Also Read:


Practise This Question

In the figure below, lines XY and MN intersect at point O. If POY = 90 and A : B = 2  : 3, find ( C)2.