# Intersection of lines.

• March 19th 2008, 01:16 AM
[nuthing]
Intersection of lines.

1)find the number of intersection points of seven different lines in the plane such that no 2 of the lines are paralell and that no three of them intersect at one point.

2)four lines are given in the plane such that no 2 of them are parallel. show that the smaller angle between two of the lines does not exceed 45 degrees.

plssss can someone help me!!!(Worried)
• March 19th 2008, 05:12 AM
Soroban
Hello, [nuthing]!

Quote:

1) Find the number of intersection points of seven lines in the plane such
that no two of the lines are parallel and that no three intersect at one point.

The lines intersect "in pairs"

. . and there are: . ${7\choose2} \:=\:21$ pairs.