**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°.

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

9. A complete angle measures 360°.

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

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.