TOPICS
Search

Intangents Triangle


IntangentsTriangle

The triangle DeltaA^'B^'C^' formed by the points of pairwise intersection of the three intangents. It is not in perspective with DeltaABC.

It has trilinear vertex matrix

 [1+cosA cosA-cosC cosA-cosB; cosB-cosC 1+cosB cosB-cosA; cosC-cosB cosC-cosA 1+cosC],
(1)

or

 [a(b+c-a) (c-a)(c+a-b) (b-a)(b+a-c); (c-b)(c+b-a) b(c+a-b) (a-b)(a+b-c); (b-c)(b+c-a) (a-c)(a+c-b) c(a+b-c)]
(2)

(Kimberling 1998, p. 161).

It has side lengths

a^'=(2a^2bcr^2s)/(R^2|cosBcosC|)
(3)
b^'=(2ab^2cr^2s)/(R^2|cosCcosA|)
(4)
c^'=(2abc^2r^2s)/(R^2|cosAcosB|),
(5)

where r is the inradius of the reference triangle, s is its semiperimeter, and R is its circumradius. It has area

Delta^'=((a+b-c)^2(a-b+c)^2(-a+b+c)^2)/((-a^2+b^2+c^2)(a^2+b^2-c^2)(a^2-b^2+c^2))Delta
(6)
=(8r^2Delta^3)/(a^2b^2c^2cosAcosBcosC),
(7)

where Delta is the area of DeltaABC.

The intangents circle is the circumcircle of the intangents triangle.


See also

Extangents Triangle, Intangent, Intangents Circle

Explore with Wolfram|Alpha

References

Kimberling, C. "Triangle Centers and Central Triangles." Congr. Numer. 129, 1-295, 1998.

Referenced on Wolfram|Alpha

Intangents Triangle

Cite this as:

Weisstein, Eric W. "Intangents Triangle." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/IntangentsTriangle.html

Subject classifications