# Chapter 11 Constructions Notes for Class 9th Maths

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Chapter 11 Constructions

• Basic Constructions
• Some Constructions of Triangles
1. Use only ruler and compass while drawing constructions.
2. Protractor may be used for drawing non-standard angles.
3. Constructions of a triangle given its base, a base angle and the difference of the other two sides.
4. Constructions of a triangle given its perimeter and its two base angles.
5. A triangle can be constructed if its perimeter and two base angles are given.
6. Geometrical construction is the process of drawing a geometrical figure using only two instruments-an ungraduated ruler and a pair of compasses.
7. Some specific angles like 15°,30o,45o,60o,75o,90°, etc. can be constructed without using protractor.
8. A triangle can be constructed if its base, base angle and the sum of the two sides or the difference of the other two sides are given.