Angle trisection
![Angles may be trisected via a Neusis construction, but this uses tools outside the Greek framework of an unmarked straightedge and a compass.](/Images/godic/202502/17/Neusis-trisection.svg5716.png")
![Bisection of arbitrary angles has long been solved.](/Images/godic/202502/17/Bisection_construction5716.gif")
![Rulers. The displayed ones are marked — an ideal straightedge is un-marked](/Images/godic/202502/17/Lineale5716.jpg")
![compasses](/Images/godic/202502/17/Zirkel5716.jpg")
Angle trisection is a classical problem of compass and straightedge constructions of ancient Greek mathematics. It concerns construction of an angle equal to one third of a given arbitrary angle, using only two tools: an unmarked straightedge, and a compass.