### Constructions - Revision Notes

CBSE Class 09 Mathematics

Revison Notes
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. Construction of bisector of a Line segment using compass - Draw a line segment. With both the points of the line segment as centre and taking the radisu of more than half of the measure of line segment, draw the arcs on both sides, which cuts at two points on opposite sides. Join these two points. This line is the required bisector.
4. Construction of the bisector of a given angle - For bisecting an angle means drwing a ray in the interior of the angle, with its initial point at the vertex of the angle such that it divides the anlge into two equal parts.
5. Construction of some standard angles such as 60o, 30o, 90o, 45o, 120o, etc.
6. Constructions of a triangle  is possible if  its base, a base angle and the difference of the other two sides are given.
7. Construction of a triangle when its base, sum of the other two sides and one base angle are given.
8. Constructions of a triangle is possible if its perimeter and  two base angles are given.