Elementary Geometry for College Students (6th Edition)

The three segments of the line $\overline{AB}$ are congruent. We have trisected $\overline{AB}$
We can draw $\overline{AB}$ We can draw another line $\overline{AC}$ Using a compass, we can mark points $D, E,$ and $F$ such that $\overline{AD} \cong \overline{DE} \cong \overline{EF}$ We can connect points $B$ and $F$ We can draw parallel lines from points $D$ and $E$ to meet the line $AB$. Note that the angles at $D$ and $E$ are congruent to $\angle AFB$ Since these three blue lines are parallel, the three segments of the line $\overline{AB}$ are congruent. We have trisected $\overline{AB}$