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In the given figure, arrows marked in same direction indicate parallel lines.

Observe the figure and answer the following questions: A H G F
1. Name the polygons having 3 sides.

2. Name the polygons having 4 sides. I
3. How many polygons are there in all? 110°
B C D E
4. Write the name of the polygon ABEF.
5. Write the name of the polygon ABDH and GCEF.

Curves

We come across various plane surfaces such as the top of a table, a page of a book, etc. Now, if we
take a pencil and doodle on a page without lifting the pencil from the paper and without retracing
any portion of the drawing except at a single point. The picture thus obtained represents a curve.

Some of them can be closed curves and some will be open curves. A straight line is also an open
curve.
The flow chart given alongside classify the curves. Curves

• A curve that does not cross itself is called a
Simple curves
simple curve. (Curves that do not Non-simple curves
intersect themselves)
• A curve that does not begin and end at the same
point is called an open curve. Open curves Closed curves

• A curve that begins and end at the same point
is called a closed curve.
• A closed curve that crosses itself at different points except its endpoints is called a non-simple
closed curve.

Example 1: In the following figures, identify the open and closed curves.

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

(f) (g) (h) (i)

Solution: A curve that does not begin and end at the same point is called an open curve. Therefore,
(a), (d), (e), (g) and (h) are open curves.
A curve that begins and ends at the same point is called a closed curve. Therefore, (b), (c), (f), and
(i) are closed curves.

55 Quadrilaterals