Goldman's Transformation Puzzle

Question

In an old book (*) I found an advert with a puzzle I had never seen before.

Unfortunately the book is very rare and it is hard to make out in the scanned photocopy above. I have redrawn it:

It looks a bit like the classic Tangram puzzle, but it consists of three identical trapezoid/trapezium shapes and three triangles of different sizes.

With these pieces you have to form a square, and then transform it into a triangle by moving only two pieces.

*) The book was The Arithmachinist by Henry Goldman, from 1898. It was a self-published book promoting the mechanical calculator that he invented. A pdf file of the book can be found on this page. I have not been able to find a patent, and assume that the patent application was rejected.

Answer 1

It looks like you should be able to do this as follows:

Edit: it works! Before picture:

And after picture:

Please excuse my lack of scissors. The pieces to be moved are therefore

5 and 6 as per my diagram.

Answer 2

I hope this would be of some help. The question clearly says we have independence of forming our own square 😁