**Question:**

In a quadrilateral, define each of the following:

(i) Sides

(ii) Vertices

(iii) Angles

(iv) Diagonals

(v) Adjacent angles

(vi) Adjacent sides

(vii) Opposite sides

(viii) Opposite angles

(ix) Interior

(x) Exterior

**Solution:**

(i) In a quadrilateral $\mathrm{ABCD}$, the four line segments $\mathrm{AB}, \mathrm{BC}, \mathrm{CD}$ and DA are called its sides.

(ii) The vertices of a quadrilateral are the corner $s$ of the quadrilateral. A quadrilateral has four vertices.

(iii) The meeting point of two sides of a quadrilateral is called an angle. A quadrilteral has four angles.

(iv) In a quadrilateral $\mathrm{ABCD}$, the line segments $\mathrm{AC}$ and $\mathrm{BD}$ are called its diagonals.

(v) The angles which have a common side as their arm are called adjacent angles.

(vi) Two sides are adjacent if they have a common end point.

(vii) Two sides are opposite if they do not have a common end point.

(viii) The two angles of a quadrilateral which are not adjacent are called opposite angles.

(ix) The part of the plane made up by all such points that are enclosed by quadrilateral is called the interior.

(x) The part of the plane made up by all the points that are not enclosed by quadrilateral is called the exterior.