[b]Check boxes for the following:[/b][br]1. Show tangents from point C to circle,[br]2. Show line segments OC[br][br][b]Red dots for :[/b][br]1. Moving the external point, C.

[b]Pre-requisite knowledge and terms:[/b] Pythagoras Theorem, Perpendicular bisector, Radius, Chords, Tangents[br][br][b]Task: [/b]How do you prove that the tangents from the external points are equal in length?[br][br](Hint: You may want to select "Show tangents from point C to circle". Besides the tangents, what are the dotted lines? What do they have in common? Select the check box "Show line segment OC" and recall the relationship between the sides in a pythagoras theorem. What is common between the 2 triangles, triangles OCD and OCE? Apply Pythagoras Theorem.)