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.