Theorem of Thales
Below you can see a triangle whose vertex C lies on a semicircle over segment c.
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Drag point C with the mouse along the semicircle and watch the
angles of the triangle. Write down your observations on a sheet of
paper.
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Use the Angle tool to create the angles of the triangle. Check your
assumptions from 1) by moving point C with the mouse (in Move mode).
Judith Preiner, Created with GeoGebra
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