Page 185 - ICSE Math 6

Example 1: Classify the given polygons on the basis of number of sides.

(a) (b) (c) (d)

Make two more figures of each of the above type.

Solution: (a) A quadrilateral (b) A triangle

(c) A pentagon (d) An octagon

A diagonal is a line segment that joins any two vertices of a polygon and is not a side of the polygon.

Example 2: Draw a rough sketch of a pentagon and draw its diagonals. How many diagonals are
formed? E

Solution: AC, AD, BD, BE and CE are the diagonals of A D
pentagon ABCDE. In all, there are 5 diagonals.

B C
Triangle P

A triangle is a polygon with three sides. A triangle can also be seen as a closed
figure enclosed by three line segments. The region enclosed by a triangle
is known as the triangular region. A triangle is denoted by the symbol Triangular
‘D’. So, the adjoining figure can be called as DPQR (read as triangle PQR). Q region R

Parts of a triangle

Sides
The line segments forming a triangle are known as its sides. In DPQR, PQ, QR and PR are its sides.

Vertices
The point of intersection of any two sides of a triangle is known as its vertex. For example, P, Q and
R are the vertices of DPQR. We can relate a side by a vertex. For example, in DPQR, P is the vertex
opposite to the side QR, Q is the vertex opposite to the side PR and R is the vertex opposite to the
side PQ.

Interior and exterior of a triangle
The triangular region of a triangle is its interior and the region outside the triangle is its exterior.

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