angle trisection
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construction of an angle equal to one third a given angle
~17 min read
Encyclopedic overview
Angles may be trisected via a neusis construction using tools beyond an unmarked straightedge and a compass. The example shows trisection of any angle θ > 3π/4 by a ruler with length equal to the radius of the circle, giving trisected angle φ = θ/3.
Angle trisection is the construction of an angle equal to one third of a given arbitrary angle, using only two tools: an unmarked straightedge and a compass. It is a classical problem of straightedge and compass construction of ancient Greek mathematics.
Excerpted from Wikipedia’s “angle trisection” article, available under the CC BY-SA 4.0 licence.