Page 127 - ICSE Math 5

Geometry
9 Geometry

Learning Outcomes

Students will be able to learn:
 about angles and their measures.
 the classification of angles: right, acute, obtuse and straight angles.
 about the symmetry in 2D and 3D shapes.
 the reflection and rotational symmetry with respect to 2D shapes.
 to identify the nets of 3D shapes or solids.

Let’s revise some basic geometrical terms.
• A point is just a dot made on paper. It has no shape or size. It is the smallest geometrical
shape. The points are denoted by letters like A, B and K.

• • •
A B K
• A line can be extended to any length on both the sides. It has no starting point or end point.

The line shown below is line AB and is denoted as AB. A line cannot be measured as it has
no fixed length.

A B

A line can be broadly categorized into two main types.

Straight lines Curved lines

A A
Vertical Slanting Horizontal
line B line B line A B

Sides of this page are examples of straight line.
Edge of a bangle is an example of curved line.

We know that besides being straight and curved, two or more lines can be intersecting,
parallel or perpendicular.

Intersecting lines are two or more lines which cross each other at A C
a common point. In the figure given alongside, O is the common
point where the two lines AB and CD meet. The common point O O
is called the point of intersection. All the intersecting lines form
angles at the point of intersection. D B

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