Lesson Thirty-Sixth Parts of the Circle
The part of the circle bounded by the chord a b and the arc a b is called a segment.
Read three segments, each less than half a circle, thus,—the segment bounded by the chord a d and the arc a b d.
A segment is a part of a circle bounded by an arc and a chord.
Read two segments that are each half a circle.
What is the chord called?
What is the arc called?
A segment bounded by a diameter and a semi-circumference is a “semicircle.”
A semicircle is half a circle.
Read four segments each larger than a semicircle.
The part of the circle between the two radii o f, o i, and the arc f i, is called a “sector.”
Read four sectors each less than one-fourth of a circle.2
A sector is a part of a circle bounded by two radii and an arc.
What part of the whole circle is the sector f o h?
It is called a “quadrant.”
A quadrant is a sector which is one-fourth of a circle.
Read a sector which is greater than a quadrant.
If the chord e f be regarded a diameter, what do you call the semicircle below it?
If it be regarded as two radii, what is the semicircle called?
Then a semicircle is both a segment and a sector.
Notes
2. Thus, a sector bounded by the two radii o g, o h, and the arc g h.