Let us first consider a plane.

The surface of a blackboard, a kitchen table and a notice board lies on

a plane.

Now, let us recall about line segments.

The following figures denote a straight line segment and a curved line

segment.

In mathematics, figures drawn on flat surfaces using straight line

segments and curved line segments are defined as plane figures. Given

below are some plane figures.

Plane figures such as the following three figures which are completely

bounded by line segments are defined as closed plane figures.

Plane figures such as the following figures which are not completely

bounded by line segments are called open figures.

(1) Select the closed plane figures from the following figures and write

down the corresponding letters.

Given below are some examples of closed figures bounded by straight

line segments only. Such figures are called closed rectilinear plane

figures.

(1) Select the rectilinear plane figures from the following figures and

write down the corresponding letters.

An angle formed inside a rectilinear plane figure by two sides meeting

is defined as an angle of the plane figure.

Next, let us look at closed rectilinear plane figures drawn with three

straight line segments and drawn with four straight line segments in

detail.

A closed rectilinear plane figure drawn with three straight line segments

is defined as a ''triangle''.

A closed rectilinear plane figure drawn with four straight line segments

is defined as a ''quadrilateral''.

• Various types of quadrilaterals and their properties

It is possible to distinguish acute angles, right angles and obtuse angles

by using a right angled corner. Also, when a rectilinear plane figure

has been drawn on a square grid, the length of a side and the gap

between opposite sides can be found by counting the number of squares

(appropriately).

In the above quadrilateral,

2 the length of each side in blue is 9 squares.

2 the length of each side in red is 7 squares.

2 all angles are right angles.

2 the gap between the pair of sides in blue is 7 squares.

2 the gap between the pair of sides in red is 9 squares.

Now let us engage in an activity and identify various types of

quadrilaterals and their properties.

(1) From the plane figure names given below each figure, select the suitable name

and mark ✔️ or ❌ appropriately within brackets.

(2) Draw two figures of each of the following types of rectilinear plane

figures on your square ruled exercise book.

(i) Square (ii) Rectangle (iii) Parallelogram (iv) Trapezium

(3) A window grill design drawn on a square ruled paper is given below.

(i) Copy this design onto your exercise book.

(ii) Identify each of the following rectilinear plane figures in the grill

design you copied and using different colours for the different

shapes, colour a figure of each type.

(a) Triangle (b) Square (c) Parallelogram (d) Trapezium