[color=#0000ff][b]■ If AB ≠ BC[/b][/color][br]Such case, we need 7 bars.[br]( cf. [url=https://www.geogebra.org/m/JKnvhyBa]Exact straight line by general square.[/url] )[br][br]AB = BC condition causes the simplicity. (points A, C are shared by [color=#00ff00][b]Green bars[/b][/color].)[br][br][color=#0000ff][b]■ AC // M'M is very important trick[/b][/color][br]In above sample, M is the middle point of CD. 　 i.e. ratio is 0.5.[br]But, any ratio is OK, of course.[br][br]△CHA ∽ △MGM' --- so, HA // GM' --- so, HA // M'G'[br][br][b][color=#0000ff]■ Imai's Low of cosines frame.[br][/color][/b]This tool is educational for students.[br]I named this method [b][color=#ff0000]"Imai's Low of cosines frame"[/color][/b], as a memento. [br][br]This method is simpler than [b][color=#ff0000]"Hart's Inversor"[/color][/b] or [b][color=#ff0000]"Hart's A-frame" [/color][/b]methods, I think so.[br][br][color=#ff00ff]But as a result, this tool is same as Hart's Inversor apparatus. [br]That is, different approach, different proof.[/color]