 Manipulative 1: Line as a locus of points. Created with GeoGebra. 

A locus is a set of points that satisfy a
condition.^{[1]} The points may be continuous. For example, a line is the locus of all points
equidistant
from two points.
Click on the blue points in manipulative 1 and drag them to change the figure. Points
A and B are the points on which the line is defined. Dragging
point C draws the line composed of points equidistant from points A and
B.
Manipulative 2 is the locus of all points equidistant from a center. Click on
the blue point in manipulative 2 and drag it to see the locus.

 Manipulative 2: Locus of points equidistant from a center. Created with GeoGebra. 
