Jernita Randolph

Creating a Script Tool for Tangent Circles

Here we will demonstrate the steps to creating a script tool for tangent circles using Geometry Sketch Pad. We begin our construction with two arbitrary circles where the smaller circle c₂ with radius B lies within the interior, but not touching the larger circle c₁ with radius A.

Now we will place an arbitray point C on the larger circle. We want to create a new circle c₃ with the same radius of the smaller circle c₂ and center C. We can do this by constructing a radius in circle c₂ and using the measure of that radius and the point C to construct a circle or we can simply copy the circle c₂ at the point C. Also, let’s construct the line through point C and center A. Next, let the point where this third circle intersects the line through points C and A be called point D.

We will now construct the line segment from B to D and find the midpoint (M) of this segment. Now construct the perpendicular bisector of segment BD by constructing a perpendicular through point M. The point where the perpendicular bisector intersects the line AC will be labeled E.

Now we can construct an isosceles triangle BED, which is pictured in gold.

We can now construct a tangent circle whose center is the vertex of the isosceles triangle with a radius of segment CE. The tangent circle is pictured in Magenta.

To create a script tool for tangent circles, select the sketch either by going to edit select all or dragging a box around the sketch and then go to script tools on the toolbox. Select “create new tool” and then name the file and save. You may choose to hide some of the lines before making the sketch a script tool.

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