• A point determines a location. It is usually denoted by a capital letter.

• A line segment corresponds to the shortest distance between two points. The line segment joining points A and B is denoted by AB . AB and BA denote the same line segment.

• A line is obtained when a line segment like AB is extended on both sides indefinitely; it is denoted by AB or sometimes by a single small letter like l.

• Two distinct lines meeting at a point are called intersecting lines.

• Two lines in a plane are said to be parallel if they do not meet.

• A ray is a portion of line starting at a point and going in one direction endlessly.

• Any drawing (straight or non-straight) done without lifting the pencil may be called a curve. In this sense, a line is also a curve.

• A simple curve is one that does not cross itself.

• A curve is said to be closed if its ends are joined; otherwise it is said to be open.

• A polygon is a simple closed curve made up of line segments. Here,

(i) The line segments are the sides of the polygon.

(ii) Any two sides with a common end point are adjacent sides.

(iii) The meeting point of a pair of sides is called a vertex.

(iv) The end points of the same side are adjacent vertices.

(v) The join of any two non-adjacent vertices is a diagonal.

• An angle is made up of two rays starting from a common end point.

• Two rays OA OA and OB make ∠AOB (or also called ∠BOA ).

• An angle leads to three divisions of a region:

• On the angle, the interior of the angle and the exterior of the angle.

• A triangle is a three-sided polygon.

• A quadrilateral is a four-sided polygon. (It should be named cyclically). In any quadrilateral

ABCD, AB & DC and AD & BC are pairs of opposite sides. ∠A & C and ∠ ∠B & ∠D are pairs of opposite angles. ∠A is adjacent to ∠B & D∠ ; similar relations exist for other three angles.

• A circle is the path of a point moving at the same distance from a fixed point. The fixed point is the centre, the fixed distance is the radius and the distance around the circle is the circumference.

• A chord of a circle is a line segment joining any two points on the circle.

• A diameter is a chord passing through the centre of the circle.

• A sector is the region in the interior of a circle enclosed by an arc on one side and a pair of radii on the other two sides.

• A segment of a circle is a region in the interior of the circle enclosed by an arc and a chord.

• The diameter of a circle divides it into two semi-circles.

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