Definition:Circle/Chord

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Definition

Circle.png

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