TOPICS
Search

Quantitative Monsky Problem


The quantitative Monsky problem asks how nearly an odd number of triangles in a dissection of a unit square can have equal areas. For a dissection D into n nondegenerate triangles with areas a_1,...,a_n, define

 R(D)=max_(i)a_i-min_(i)a_i,
(1)

and let

 Delta(n)=inf_(D)R(D).
(2)

The infimum is attained for every n>=2. Monsky's theorem (Monsky 1970) implies that Delta(n)>0 for every fixed odd n.

QuantitativeMonskyDissections

The dissections illustrated above contain five, seven, and nine triangles. The labels H and L indicate the larger and smaller areas, respectively. Li (2026) proved the exact value

 Delta(5)=(5sqrt(5)-11)/8.
(3)

Every minimizing dissection into five triangles has three triangles of area (3-sqrt(5))/4 and two triangles of area (3sqrt(5)-5)/8. For seven triangles,

 Delta(7)=r_7=0.0002011756316409390820...,
(4)

where r_7 is the unique root in (0,1/4900) of

 864r^4+2160r^3-6060r^2+4972r-1=0.
(5)

Every minimizing dissection into seven triangles has four triangles of area (1+3r_7)/7 and three triangles of area (1-4r_7)/7.

Li (2026) also constructed a dissection into nine triangles proving

 Delta(9)<=r_9=0.0001273496861283553341...,
(6)

where r_9 is the unique root in (0.000127,0.000128) of

 4864r^4-824r^3-18804r^2-7850r+1=0.
(7)

This construction has five triangles of area (1+4r_9)/9 and four triangles of area (1-5r_9)/9. The value r_9 is the exact minimum within the tilted-strip construction, but the exact value of Delta(9) remains open.

Li (2026) reports that OpenAI GPT models accessed through ChatGPT and Codex contributed substantially to refining the research program, exploring constructions, developing proof decompositions, and designing and auditing the verification code. The author selected and checked the final statements, arguments, and code and assumes responsibility for the results.


See also

Dissection, Square, Triangle

Explore with Wolfram|Alpha

References

Li, M. "Exact Area-Range Minima in the Quantitative Monsky Problem for Five and Seven Triangles: Computer-Assisted Certification, a Nine-Triangle Upper Bound, and Limits of the Single-Cap Zig-Zag Family." 19 Sep 2026. https://arxiv.org/abs/2609.22693.Monsky, P. "On Dividing a Square into Triangles." Amer. Math. Monthly 77, 161-164, 1970.

Cite this as:

Weisstein, Eric W. "Quantitative Monsky Problem." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/QuantitativeMonskyProblem.html

Subject classifications