Definition:Circle/Chord
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Definition
A chord of a circle is a straight line segment whose endpoints are on the circumference of the circle.
In the diagram above, the lines $CD$ and $EF$ are both chords.
Thus a chord is a line segment joining the endpoints of an arc of the circle.
Note that under this definition, the diameter itself is in fact a chord.
In the words of Euclid:
- A straight line is said to be fitted into a circle when its extremities are on the circumference of the circle.
(The Elements: Book $\text{IV}$: Definition $7$)
Sources
- 2008: Ian Stewart: Taming the Infinite ... (previous) ... (next): Chapter $5$: Eternal Triangles: The origins of trigonometry