– = –1–1–6– –1; +5 –6–6 + 5 – 6 = –1. (–6) + (+5) = (+ 5) + (– 6) a + b = b + a
– = –1–1 –6– ; (–6) + (+5) + (+6) = (a + b) + c = a + (b + c) = (+5) + (–6) + (+ 6) = = (+5) + (–6) + (+ 6) ( )