**Point:**

A point is that which has no part. A point is represented by a fine dot made by a sharp pencil on a sheet of paper.

**Plane:**

The surface of a smooth wall or the surface of a sheet of paper or the surface of a smooth black board is close examples of a plane.

**Line:**

A line is breadth less length e.g., the edge of a ruler, the edge of the top of a table, the meeting place of two walls of a room is also examples of a geometrical straight line.

**Collinear Points:**

· Three or more points are said to be collinear, if there is a line that contains all of them.

**Concurrent Lines:**

· Three or more lines are said to be concurrent, if all of them pass through a common point.

· Two distinct lines cannot have more than one point in common.

**Intersecting Lines:**

·Two lines who meet at one point are said to be intersecting lines. The common point is called the ‘point of intersection’.

**Parallel Lines:**

· Two lines *l* and m in a plane are said to be parallel lines, if l Ç m = f . If l and m are parallel lines in a plane then denote as l || m .

· Two lines which are both parallel to the other line then all lines are parallel to each other.

· If *l*, m, n are lines in the same plane such that *l* intersects m and n || m, then *l* intersects n also.

· If *l* and m are intersecting line, *l* || p and q || m, then p and q also intersect.

**Intercept Theorem:**

· If a transversal makes equal intercepts on three or more parallel lines, any other line cutting them will also make equal intercepts.

Hence, AC/CE = BD/DF