12 х 45 = [ 10 + 2 ] x 45 = 10 x 45 + 2 x 45 = 450 + 90 = 540- распределительный закон
12 x 45 = 12 x [ 50 - 5 ] = 12 x 50 - 12 x 5 = 600 - 60 = 540
12 x 45 = 12 x [ 5 x 9 ] = [ 12 x 5 ] x 9 = 60 x 9 = 540 -сочетательный закон
12 x 45 = [ 3 x 4 ] x 45 = 3 x [ 4 x 45 ] = 3 x 180 = 540