| 释义 | 
		Triangle Inscribing in a CircleSelect three points at random on a unit Circle.  Find the distribution of possible areas. The first point can beassigned coordinates (1, 0) without loss of generality.  Call the central angles from the first point to the second andthird   and  . The range of   can be restricted to [0,  ] because of symmetry, but  can range from  . Then
    | (1) |  
  so
   | (2) |  
  where 
   | (3) |  
  Therefore,
 
 
 But  Write (4) as
    | (6) |  
  then
   | (7) |  
  and
   | (8) |  
  From (6),
 
  so
   | (10) |  
  Also,
 
  so
   | (12) |  
  Combining (10) and (12) gives
   | (13) |  
  The Variance is
 
  See also Point-Point Distance--1-D, Tetrahedron Inscribing
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