Henry Ernest Dudeney/Puzzles and Curious Problems/186 - Triangle and Square/Solution

Puzzles and Curious Problems by Henry Ernest Dudeney: $186$

Can you cut each of two equilateral triangles into three pieces,

so that the six pieces will fit together and form a perfect square?

Cut one triangle in half, and place the pieces together as in Figure $1$.

Now cut along the dotted lines, making $ab$ and $cd$ each equal to the side of the square we are making.

Then fit together the pieces as in Figure $2$, sliding the pieces $F$ and $C$ upwards to the left, bringing down $D$ to fill that gap in the corner.

Martin Gardner reports that Harry Lindgren has discovered a $5$-piece dissection.

This appears in his $1964$ work Geometric Dissections.