GEAR UP FOR LIFE

MATH MENTOR: Geometry Part 1: Lines

 

Geometry is full of lines and curves or circles.

A straight line is one of the basic terms in geometry.

Most of us say, "A line is something straight that we draw with a ruler. It has a beginning and an end." Yes, but in geometry, a line extends forever in both directions.

Line Segments

Lines go forever. Line segments have a beginning and an end. In geometry, line segments (pieces or parts) have names. A segment is the part of the line between two points. We write the name of a line passing through two different points, A and B, as "line AB" or as . The arrows over AB mean that a line is passing through points A and B.

Example: The following is a diagram of two lines: line AB and line CD

The Dots

In geometry, the dots or points just tell you where the letters are. They don't mean anything geometric. They just show location.

Intersections

Sometimes, segments meet as they cross each other. The point where they meet each other, is called and intersection. That is like two streets that cross each other at the intersection.

Line CD intersects AB at G.

Example: Line 1 intersects the circle at point G. Line 2 intersects the rectangle at points D and C.

Rays

Sometimes in geometry you will see a line that starts at a certain point but goes forever. That type of line is called a ray. The point where a ray begins is called an end point.

A line segment has two end points. A ray has one.

If you are referring to ray AB, you would use the following symbol:

Parallel Lines

Two lines next to each other which never intersect are called parallel lines. If line 1 is parallel to line 2, we write this as

line 1 || line 2

When two line segments, DC and AB, lie on parallel lines, we write this as

segment DC || segment AB.

Example: 

Lines 1 and 2 below are parallel.

 

 

Segments AB and CD below are parallel

 

 

 

A square and a rectangle have parallel sides. Their opposite sides never meet.

Name the symbols using the boxes provided. (For example: ray GH or segment AB)
1.           
2.   

 

    

3.      
4.      
5.      

 

6.      

 

7. line 1 || line 2      

 

 

Go to Geometry Part 2: Angles