### 26.17.3 Trace of a geometric object

The trace command draws the trace of an object.

- trace takes G, a geometric object which depends on a parameter.
- trace(G) draws the trace of G as the parameter is changed or the object is moved in Pointer mode.

#### Example

For example, to find the locus of points equidistant from a line d and a point F, you can create a point H on the line d. To do this, open a graphic window (Alt+G) and type in the following commands.

First, create a line d (using sample points) and a sample point F.

A,B:=point(-3-i),point(1/2+2*i); d:=line(A,B,color=0); F:=point(4/3,1/2,color=0)

Then create a point H on the line d which you can move around.

assume(a=[0.7,-5,5,0.1]); H:=element(d,a)

To find a point equidistant from d and F, find the point M where the perpendicular to d (at H) intersects the perpendicular bisector of HF, and trace that point.

T:=perpendicular(H,d); M:=single_inter(perpen_bisector(H,F),T)); trace(M)

Then as the point H on the line moves (by changing the value of a with the slider), you will get the trace of M.

To erase traces, add traces, activate or deactivate them, use the Trace menu of the M button located on the right side of the geometry screen.