Math A

What is a
Locus?

 

A locus is a set of points which satisfies a certain condition.  

Think of a locus as a "bunch" of points that all do the same thing.
In Latin, the word locus means place.
The plural of locus is loci.

 

There are five basic locus theorems (rules). 
 Each theorem will be explained in detail in the following sections
under this topic.  Even though the theorems sound confusing,
the concepts are easy to understand.

 Click on each theorem to see the theorem statement.  Be sure to close each pop up box before continuing.

Locus Theorem 1 (point)

Locus Theorem 2 (line)

Locus Theorem 3 (two points)

Locus Theorem 4 (parallel lines)

Locus Theorem 5 (intersecting lines)

 

Steps to solving a locus problem:
1.  Draw a diagram showing the given lines and points.

2.  Read carefully to determine the needed condition.

3.  Locate one point that satisfies the needed condition and plot it on your diagram.  Locate several additional points that satisfy the condition and plot them as well.  Plot enough points so that a pattern (a shape) is starting to appear.

4.  Through these plotted points draw a dotted line to indicate the locus (or path) of the points.

5.  Describe in words the geometric path that appears to be the locus.

6.  If TWO conditions exist in your problem (a compound locus), repeat steps 2-4 above for the second condition ON THE SAME DIAGRAM.   Count the number of points where the two loci intersect.  (Where do the dotted lines cross?)

 

Remember:
A locus is just a set of points.

 

 

 

BackMath.gif (4139 bytes)


Roberts