Maths Chapter 05: Understanding Elementary Shapes
Class 06 Maths NCERTThe 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 1⁄4 revolution and a straight angle is 1⁄2 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:
- 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:
- 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.
- 3 - Triangle
- 4 - Quadrilateral
- 5 - Pentagon
- 6 - Hexagon
- 8 - Octagon
Quadrilaterals are further classified with reference to their properties.
- 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
Three dimensional shapes: Cubes, cuboids, spheres, cylinders, cones, prisms and pyramids are some of them.