CBSE · Class 6-12

Class 9 · Ganita Manjari

Unit 12 · Class 9Ganita Manjari

Quadrilaterals

Four-sided figures — angle sum, and the family tree from parallelogram down to square.

Lessons

3 concepts

1
Why 360°
Split any quadrilateral along one diagonal into two triangles. Each triangle has angle sum $180^\circ$ , so the quadrilateral has $360^\circ$ .
2
The Family Tree
Square $\subset$ Rhombus $\subset$ Parallelogram; Square $\subset$ Rectangle $\subset$ Parallelogram. A square inherits every property of a rectangle AND a rhombus.
3
Diagonals as a Diagnostic Tool
Diagonals of a **parallelogram** bisect each other. Add **equal diagonals** — you get a rectangle. Add **perpendicular diagonals** — you get a rhombus. Add both — you get a square.

Skills to practise

Skill · medium

Quadrilaterals — Practice