With three cuts, dissect an equilateral triangle into a square. The problem was first proposed by Dudeney in 1902, and subsequently discussed in Dudeney (1958), and Gardner (1961, p. 34), Stewart (1987, p. 169), and Wells (1991, pp. 61-62). The solution can be hinged so that the four pieces collapse into either the triangle or the square. Two of the hinges bisect sides of the triangle, while the third hinge and the corner of the large piece on the base cut the base in the approximate ratio 0.982:2:1.018.
Haberdasher's Problem
See also
DissectionExplore with Wolfram|Alpha
References

Referenced on Wolfram|Alpha
Haberdasher's ProblemCite this as:
Weisstein, Eric W. "Haberdasher's Problem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/HaberdashersProblem.html