43²/144-43×31/72+31²/144 = 1849/144-1333/72+961/144 = 1849/144-2666/72+961/144 = 144/144 = 1
(43/12)^2-2•43•31/144+(31/12)^2=(43/12-31/12)^2=12/12^2=1
