### Understanding Elementary Shapes-Revision Notes

CBSE Class 6 Mathematics

Revision Notes

CHAPTER – 5

Understanding Elementary Shapes

Revision Notes

CHAPTER – 5

Understanding Elementary Shapes

- The distance between the end points of a line segment is its length.
- A graduated ruler and the divider are useful to compare lengths of line segments.
- When a hand of a clock moves from one position to another position we have an example for an angle.
- One full turn of the hand is 1 revolution.
- A right angle is ¼ revolution and a straight angle is ½ a revolution.
- We use a protractor to measure the size of an angle in degrees.
- The measure of a right angle is 90° and hence that of a straight angle is 180°.
- An angle is acute if its measure is smaller than that of a right angle and is obtuse if its measure is greater than that of a right angle and less than a straight angle.
- A reflex angle is larger than a straight angle.
- Two intersecting lines are perpendicular if the angle between them is 90°.
- The perpendicular bisector of a line segment is a perpendicular to the line segment that divides it into two equal parts.
- Triangles can be classified as follows based on their angles:

Nature of angles in the triangle | Name |

Each angle is acute | Acute angled triangle |

One angle is a right angle | Right angled triangle |

One angle is obtuse | Obtuse angled triangle |

- Triangles can be classified as follows based on the lengths of their sides:

Nature of sides in the triangle | Name |

All the three sides are of unequal length | Scalene triangle |

Any two of the sides are of equal length | Isosceles triangle |

All the three sides are of equal length | Equilateral triangle |

- Polygons are named based on their sides.

Number of sides | Name of the Polygon |

3 | Triangle |

4 | Quadrilateral |

5 | Pentagon |

6 | Hexagon |

8 | Octagon |

- Quadrilaterals are further classified with reference to their properties.

Properties | Name of the Quadrilateral |

One pair of parallel sides | Trapezium |

Two pairs of parallel sides | Parallelogram |

Parallelogram with 4 right angles | Rectangle |

Parallelogram with 4 sides of equal length | Rhombus |

A rhombus with 4 right angles | Square |

- ·We see around us many three dimensional shapes. Cubes, cuboids, spheres, cylinders, cones, prisms and pyramids are some of them.