Tangent Circle GSP Tool Construction

By Laura Lowe

Construct two circles. I placed mine one inside the other to
begin with to make it easier to create the tool. Later I can move it around and see what happens.

Now create a point on the
outer circle, A, and construct a line through the center and A. Construct a radius of the inner circle.

Now construct a circle,
congruent to the inner circle, where the line intersects the outer circle. Mark where the line intersects the new
circle, outside the circle, and call it B.

Now construct the line
segment BE, and the perpendicular bisector. Mark the intersection of the perpendicular bisector D.

D is the center of the circle
tangent to our original circle.
The radius of the circle is DA.
Construct the circle.

Notice the isosceles
triangle. (Remember this –
it is important)

Last, hide everything except
the circles, and create your tool.
Here
is mine.