To insert a straight line equal to a given straight line into a circle, (the latter straight line) not being greater than the diameter of the circle. * Let $ABC$ be the given circle, and $D$ the given straight line (which is) not greater than the diameter of the circle. * So it is required to insert a straight line, equal to the straight line $D$, into the circle $ABC$.
It is possible to construct a chord of a circle with a length less or equal to the diameter.
Proofs: 1