In 1907, the English author and mathematician Henry Ernest Dudeney posed a puzzle: Can any equilateral triangle be cut into as few pieces as possible that will fit together to form a perfect square?

A geometry problem over a century old has just found its definitive answer. Mathematicians have confirmed that the solution proposed by Henry Dudeney in 1907 was indeed the most efficient possible.

Dudeney’s original solution for transforming an equilateral triangle into a perfect square through dissection involves only four pieces, a solution that has now been proved to be the optimal solution.