# name of a shape

Let P be a point, not the center, in the interior of a (round) disk D⊂ℝ² and let A and B be points on ∂D such that the line segments AP and BP have equal length. Choose an arc AB. What's the shape bounded by the arc and the two segments called?

• For $P$ at the center, that's a "sector". ( en.wikipedia.org/wiki/Circular_sector ) I don't know of a name for $P$ elsewhere. How about "pseudo-sector" or "generalized sector"? (BTW, this might be a cleaner description: Given P on the diameter bisecting arc AB, the figure bounded by AP, BP, and arc AB.) – Blue Jan 10 '11 at 0:02
• What leads you to believe that this object should have a name? – Tpofofn Jan 10 '11 at 1:07
• I call this a "slice" ;) – Matt Calhoun Jan 10 '11 at 1:25
• @Jasper Loy "By '(round) disk' do you simply mean circle", well, a circle is one-dimensional; I meant the thing it bounds. – msh210 Jan 10 '11 at 16:39
• @Day Late Don "a cleaner description": Yes, thanks! – msh210 Jan 10 '11 at 16:42

## 2 Answers

I suppose you could call it an isosceles curvilinear triangle, although that doesn't capture the curvy part being an arc of a circle.

It's called a circular segment.

Edited to add: As Jasper has pointed out in the comments, this is not what the question asked. So I don't know the answer.

• I'm pretty sure that a circular segment is only the region between a chord AB and minor arc AB. – Isaac Jan 9 '11 at 21:42
• @Isaac: Yes, my Wikipedia link agrees with you. It looks as if the region between a chord AB and major arc AB doesn't have a name. How about 'circular cosegment'? – TonyK Jan 9 '11 at 22:17
• If you "don't know the answer", please delete your answer. – Lord_Farin Nov 26 '13 at 9:17
• @Lord_Farin: I don't know what inspired you to check back through almost three years of my answers, but I'm sure it's not healthy... – TonyK Nov 26 '13 at 9:38
• @TonyK Someone else did. It showed up in the 10k Tools. Rest assured, it's nothing personal. – Lord_Farin Nov 26 '13 at 9:39