Locus:  At a Fixed Distance
from a Line

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Consider: 
Your teacher has placed a strip of tape on the classroom floor which forms a straight line.  The teacher gives each student a yard stick and asks that each student stand exactly 3 feet away from the line on the floor.  Can you picture what will happen?  If you, and all of your classmates, stand exactly 3 feet away from the line, describe where you and your classmates will be standing.


Answer:

You and your classmates will form two straight lines on either side of the tape on the floor,
 at a distance of 3 feet away from the tape.

You and your classmates are the locus of points equally distant (equidistant) from a given line (the tape on the floor).

 

Stated formally, we have our next locus theorem.

Locus Theorem 2: (line)

The locus of points at a fixed distance, d, from a line, l, is a pair of parallel lines d distance from l and on either side of l.

 

Note that all three of these lines are parallel.