All constructions
ABC
Try it on the Geometry BoardUses:Perpendicular from a pointBisect an angle

Excircle

Draws the circle outside a triangle that touches one side and the other two sides extended. Ruler and compass only.

All parts
Part 1 of 8: Extend AB beyond BStep 1 of 3Ruler

The excentre opposite A is outside BC. Lay the ruler along AB.

Keys: left and right arrows step, Space plays or pauses, Escape goes back to all constructions.