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.
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.
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.
· Three or more points are said to be collinear, if there is a line that contains all of them.
· 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.
·Two lines who meet at one point are said to be intersecting lines. The common point is called the ‘point of intersection’.
· 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.
· 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