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vertices, (see Fig. 18.1).

2. Terms Related to Quadrilateral
1. Opposite Sides: Two sides of a quadrilateral which do not intersect, i.e.
have no common end point (vertex) are called opposite sides. In
quadrilateral ABCD, AB, CD and BC, AD are two pairs of opposite sides.
2. Consecutive or Adjacent Sides: Two sides of a quadrilateral which have a
common point, i.e. intersect each other are called consecutive sides. In
quadrilateral ABCD, AB, BC; BC, CD;
CD, DA and DA, AB are four pairs of consecutive sides.
3. Opposite Angles: Two angles of a quadrilateral are said to be opposite
angles, if they do not have common arm. In quadrilateral ABCD, ∠A, ∠C and
∠B, ∠D are two pairs of opposite angles.
4. Consecutive or Adjacent Angles: Two angles of a quadrilateral are said to
be consecutive or adjacent angles, if they have a common arm. In
quadrilateral ABCD, ∠A, ∠B; ∠B, ∠C; ∠C, ∠D and ∠D, ∠A are four pairs of
consecutive angles.
5. Diagonal: In a quadrilateral, the line segment joining the opposite vertices is
called a diagonal of the quadrilateral. In quadrilateral ABCD, AC and BD are
two diagonals.
3. The sum of the four angles of a quadrilateral is 360°.

Procedure

1. Take a piece of rectangular cardboard of suitable size and by using adhesive,
paste a white paper on it.

2