With a simple swivel, the pieces spun around to transform the triangle into a square. The exhibit traces its origin to a mathematical puzzle published in a 1902 newspaper. Henry Dudeney ...

Below are some of my go-to quilting tools. I have found a half square triangle ruler to be so very helpful when quilting. And ...

Use a pen and ruler to draw over the vertical lines and join the dots, giving you a square. Image caption ... you now have a regular equilateral triangle.