Page 62 - Maths Class 06

D
In quadrilateral ABCD, AB, BC, CD and DA are its sides, and PQ QR RS, , and SP
are sides of the quadrilateral PQRS.

A line segment joining the opposite vertices of a quadrilateral is called the
diagonal of the quadrilateral. In quadrilateral ABCD, AC and BD are is two C
diagonals. A
The four angles Ð ABC, ÐBCD, ÐCDA and ÐDAB which are formed by joining
the line segments AB BC CD, , and DA are the angles of quadrilateral ABCD. We
B
can write them as ÐB, ÐC, ÐD and Ð A respectively. Fig. 4.22
Adjacent Sides and Opposite Sides of a Quadrilateral

Two sides of a quadrilateral having a common endpoint are called adjacent sides.

In Fig 4.22, AB and BC are adjacent sides because point B is common to both of them. So are BC and
CD CD, and DA DA, and AB.
The sides which are not adjacent are called opposite. In Fig 4.22, AB is opposite to CD, and BC is opposite
to AD.

Adjacent Angles and Opposite Angles of a Quadrilateral

Two angles of a quadrilateral are said to be adjacent, if they have a side in common. In the quadrilateral
ABCD, Ð Aand Ð B form a pair of adjacent angles having the side AB in common. Similarly, other pairs of
adjacent angles are ÐB and ÐC; ÐC and ÐD; ÐD and Ð A.

Two angles of a quadrilateral are said to be opposite, if they are not adjacent angles. In Fig 4.22, Ð A and
ÐC, and ÐB and ÐD are two pairs of opposite angles.

Interior and Exterior of a Quadrilateral
R
In the plane of the quadrilateral ABCD shown in Fig. 4.23, six points P Q R S T, , , , A S B
and U are marked. P and Q are said to be in the interior of the quadrilateral ABCD;
S and U are on the quadrilateral; while R and T are in the exterior of the
Q P
quadrilateral ABCD.
The interior of a quadrilateral ABCD along with the quadrilateral ABCD is called
D V C
the quadrilateral region of ABCD, i e. . P Q S V A B C, , , , , , and D are points in the T
quadrilateral region of the quadrilateral ABCD. Fig. 4.23

Circle
You must have seen the wheels of your cycle, the wheels of a car, bangles and certain coins, what is the
shape of these things? These things are circular in shape.
Take any coin, keep it on a plain paper and with the help of a sharpened pencil draw its boundary. The
figure so obtained is called a circle. Thus, a circle is the set of all those points in a plane whose distance
from a fixed point remains constant.

Parts of a Circle
Centre : A circle is described when a point P moves in a plane, such that its distance from a fixed point in
the plane remains constant. The fixed points is called the centre of the circle. In Fig. 4.24, O is the centre
of the circle.

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