Page 59 - Maths Class 06

Interior and Exterior of an Angle
The shaded portion can be extended indefinitely between the arms OAand OB of the
Ð AOB. This portion is called the interior of the angle. Q is a point in the interior of the B
angle AOB. R
Q
Thus, the set of all those points which lie inside the angle, forms the interior of the
angle. O P A
Fig. 4.14
R is a point lying in the exterior (outside) of the angle. Thus, the set of all those points
which lie outside the angle, forms the exterior of the angle.

Ð AOB separates the interior from the exterior.

NOTE

The interior of a figure is not a limited area, as it extends indefinitely since OA and OB are rays.

Triangle
A figure bounded by three lines segments is called a triangle.
A
If A B, and C are three non-collinear points, the figure formed by joining these points is
called the triangle ABC (Fig 4.15). We use the symbol ‘D’ to denote a triangle. Therefore,
triangle ABC, can be written as D ABC. We can write D ABC as DBCA or DCAB.

The points A B, and C are the vertices of this triangle. Thus, a triangle has three vertices.
B C
The three line segments AB BC, and CA, that form the triangle ABC are called the sides of
Fig. 4.15
the triangle ABC. Thus, a triangle has three sides.

The three angles Ð ABC, ÐBCAand ÐCAB formed by joining the points A B, and C are called the angles of
the triangle ABC. For convenience, we can also denote these angles by ÐB, ÐC and Ð A respectively.
Thus, a triangle has three angles.

Ð A is the angle opposite to side BC.

ÐB is the angle opposite to side CA.
ÐC is the angle opposite to side AB.

Interior and Exterior of a Triangle
A
The shaded portion which lies inside a triangle is called interior of the triangle. In
P
Fig 4.16 points P and Q lies in the interior and points S and R lies in the exterior of the S R
Q
D ABC.

D ABC is the boundary of the interior. The interior of D ABC together with the triangle
B C
itself, is called the triangular region ABC. Fig. 4.16

Medi ans of a Trian gle
A line segment joining a vertex to the mid-point of the opposite side is called a median of the triangle.

59