(Historial note: This lab was actually delivered via email because of intermittent web server crashes.)
Work through the following lab sheets.
Trace right angles to see a special shape. The explain the reasons for what you see by looking closedly at right triangles.
Continue to explain the Carpenter Locus by showing which angles inscribed in a circle are right angles.
See how the angle formed by two intersecting tangents is related to angles formed by chords. Apply this to prove the inscribed angle theorem.
Since this concept continues to provide some difficulty, this sketch shows the main cases of similat triangles with shared angle, when the triangles are not simply dilations of each other.