Two triangles are said to be poristic triangles if they share the same incircle and circumcircle. More specifically, in the plane of a reference triangle, a triangle is said to be poristic if it has the same incircle and circumcircle as the reference triangle.
Poristic Triangles
See also
Poncelet's Porism, PorismThis entry contributed by Floor van Lamoen
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References
Brisse, E. "Perspective Poristic Triangles." Forum Geom. 1, 9-16, 2001. http://forumgeom.fau.edu/FG2001volume1/FG200103index.html.Gallatly, W. "Poristic Triangles." Ch. 3 in The Modern Geometry of the Triangle, 2nd ed. London: Hodgson, pp. 15-23, 1913.Referenced on Wolfram|Alpha
Poristic TrianglesCite this as:
van Lamoen, Floor. "Poristic Triangles." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/PoristicTriangles.html