---
source: ncert
topic: geometry
class_level: class_6
chapter: ch5
difficulty: beginner
---

Class 6 | Ch5: Understanding Elementary Shapes
Triangles by sides: Equilateral(all equal, all 60°), Isosceles(2 equal), Scalene(all different).
Triangles by angles: Acute(all<90°), Right(one=90°), Obtuse(one>90°).
Pythagorean triplets: (3,4,5),(5,12,13),(8,15,17),(7,24,25). Check: 3^2+4^2=25=5^2.
Quadrilaterals: Rectangle(4 right angles, opposite sides equal), Square(4 right angles, all sides equal), Parallelogram(opposite sides parallel equal), Rhombus(all sides equal), Trapezium(one pair parallel sides).
3D: Cube(F=6,E=12,V=8), Cuboid(F=6,E=12,V=8). Euler: F+V-E=2.
Square is special rectangle AND special rhombus. Hypotenuse=longest side opposite 90°.