NCERT Book Class 8 Mathematics (Part I) Chapter 4 Quadrilaterals

4 QUADRILATERALS

In this chapter, we will study some interesting types of four-sided
figures and solve problems based on them. Such figures are commonly
known as quadrilaterals. The word ‘quadrilateral’ is derived from Latin
words — quadri meaning four, and latus referring to sides.

Observe the following figures.

(i) (ii) (iii)

(iv) (v)

Figs. (i), (ii), and (iii) are quadrilaterals, and the others are not. Why?
The angles of a quadrilateral are the angles between its sides, as
marked in Figs. (i), (ii), and (iii).
We will start with the most familiar quadrilaterals — rectangles and
squares.