Выражения: 1) 3,9a - 2.81b - 5.1a + 4.9b 2)1 3/4x - 3 7/11y + 2 1/4x - 5 4/11y; 3) -1 5/12m - 5/7 n - 7/12 m - 2/7 n;

1) 3,9a - 2.81b - 5.1a + 4.9b = (3.9a-5.1a)+(4.9b-2.81b)= 2.09b-1.2a
2)1 3/4x - 3 7/11y + 2 1/4x - 5 4/11y = (1 3/4x + 2 1/4x) - (5 4/11y + 3 7/11y) = 4x-9y
3) -1 5/12m - 5/7 n - 7/12 m - 2/7 n = -(1 5/12m + 7/12 m) - (2/7 n + 5/7 n) = -2m-n