← GSEB Class 9
Constructions
Chapter Overview
Geometric constructions use only a compass and straightedge (unmarked ruler). Basic constructions: bisecting an angle, constructing perpendicular bisector of a line segment, constructing angles of 60°, 90°, 120°, and 45°. Constructing triangles given different criteria: SSS, SAS, ASA, RHS, and with a base and base angles. Constructing triangles with given perimeter and base angles. Constructions rely on the geometric principles of congruence and symmetry.
Topics Covered
- Angle Bisector
- Perpendicular Bisector
- Constructing Angles
- SSS Triangle Construction
- SAS Triangle Construction
- ASA Triangle Construction
- RHS Triangle Construction
- Perimeter Construction
Key Formulas
Angle bisector divides angle into two equal parts
Perpendicular bisector is equidistant from endpoints
Constructing 60° uses equilateral triangle properties
Real-World Applications
Applications: Engineering drawing, architecture plans, design, carpentry, surveying, technical illustrations.
Study Tips
Tip: Practice the basic constructions repeatedly
Tip: Learn the logic behind each construction
Tip: Maintain accurate compass settings