Many thanks for introducing!
@11011110 Coincidentally This basically method of #dissection is found in puzzle book written by "Gisaku Nakamura" (I forget book's title) https://www.amazon.co.jp/%E4%B8%AD%E6%9D%91-%E7%BE%A9%E4%BD%9C/e/B004KZ0X7G , I applied it to triangles and so on about a year ago https://twitter.com/wasanp_/status/962594728276410368 (like a attached image). Probably these first method are invented from "Mr. Henry Ernest Dudeney's hinged dissections" https://commons.wikimedia.org/wiki/File:Haberdasher-anm-01.gif , Thanks all!
By the way, in some cases it may be more suitable the another method…
For reference, Japanese Puzzler "Puzzdog's dissection method" http://puzzdoghouse.blogspot.com/2014/08/blog-post.html may be more suitable in the other case (Dudeney's method is not suitable?). For example, but not a good example https://twitter.com/wasanp_/status/954698588193304578 #etc
Although, "Puzzdog's dissection" method is suitable for converting parallelograms at equal angles #etc (cf. Attached image is a method of combining similar triangles (It is described in the book of 細矢治夫ら著『多角形百科』 https://www.amazon.co.jp/dp/4621089404/
.).). I used the method to https://mathstodon.xyz/@unknown/101280134220831493
A Mastodon instance for maths people. The kind of people who make \(\pi z^2 \times a\) jokes.
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