Class 6 Chapter 12: Understanding Elementary Shapes

Important Concepts and Formulas

1.      A line segment has two end points. The distance between the end points of a line segment is its length.

2.      Using a ruler or a divider, we can compare the lengths of two or more line segments.

3.      Points lying on the same line are called collinear points and points which do not lie on the same line are called non-collinear points.

4.      Lines which pass through the same point are called concurrent lines.

5.      The measure of a right angle is 90° and that of a straight angle is 180°.

6.      An acute angle measures between 0° and 90°.

7.      An obtuse angle measures between 90° and 180°.

8.      A reflex angle measures between 180° and 360°.  

9.      A complete angle measures 360°.

10. When two lines intersect at right angles, they are called perpendicular lines.

11. We can classify triangles based on their sides and angles.

12. In a right-angled triangle, one angle is 90° and the other two angles are acute.

13. In an obtuse-angled triangle, one angle is greater than 90° and the other two angles are acute.

14. If measures of all sides of a triangle are unequal, then it is called a scalene triangle.

15. If any two sides of a triangle are equal, then it is called an isosceles triangle.

16. If all the three sides of a triangle are equal in length, then it is called an equilateral triangle.

17. The measure of each angle of an equilateral triangle is 60°.

18. Various quadrilaterals are square, rectangle, parallelogram, trapezium and rhombus.

19. Various three-dimensional (3D) shapes are cubes, cuboids, cylinders, cones, spheres, prisms and pyramids.

20. A prism is a 3-D shape which has two identical bases and all other faces are rectangular in shape.

21. A pyramid is a 3-D shape which has only one base and all other faces are triangular in shape. The triangular faces meet at one common vertex.