Watch the following YouTube videos from Norman J. Wildberger:[br][list][*][url=https://youtu.be/xHU5aPWn8rQ]Red geometry (I) | WildTrig: Intro to Rational Trigonometry | N J Wildberger[/url][/*][*][url=https://youtu.be/-QKzBX1lOUk]Red geometry (II) | WildTrig: Intro to Rational Trigonometry | N J Wildberger[/url][br][/*][*][url=https://youtu.be/JHAWmN_IcfY]Red geometry (III) | WildTrig: Intro to Rational Trigonometry | N J Wildberger[/url][br][/*][*][url=https://youtu.be/KbcwGHG0LY4]Circles in red geometry | WildTrig: Intro to Rational Trigonometry | N J Wildberger[/url] [/*][/list]Move the points [b]A1[/b], [b]A2[/b] or [b]A3[/b] of the triangle.