Exact straight line by special square
■ If AB ≠ BC
Such case, we need 7 bars.
( cf. Exact straight line by general square. )
AB = BC condition causes the simplicity. (points A, C are shared by Green bars.)
■ AC // M'M is very important trick
In above sample, M is the middle point of CD. i.e. ratio is 0.5.
But, any ratio is OK, of course.
△CHA ∽ △MGM' --- so, HA // GM' --- so, HA // M'G'
■ Imai's Low of cosines frame.
This tool is educational for students.
I named this method "Imai's Low of cosines frame", as a memento.
This method is simpler than "Hart's Inversor" or "Hart's A-frame" methods, I think so.
But as a result, this tool is same as Hart's Inversor apparatus.
That is, different approach, different proof.