Understanding Elementary Shapes - Revision Notes
CBSE Class 6 Mathematics
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.