1)
(83a-91b)-(89a-100b) =
= 83a-91b - 89a+100b =
= (83a-89a)+(100b-91b) =
= - 6a + 9b = - 3(2a - 3b)
2)
(5k+6t)+(2.8t-3.1k) =
= 5k+6t + 2,8t - 3,1k =
= (5k-3,1k)+(6t+2,8t) =
= 1,9k + 8,8t
1)
(83a-91b)-(89a-100b) =
= 83a-91b - 89a+100b =
= (83a-89a)+(100b-91b) =
= - 6a + 9b = - 3(2a - 3b)
2)
(5k+6t)+(2.8t-3.1k) =
= 5k+6t + 2,8t - 3,1k =
= (5k-3,1k)+(6t+2,8t) =
= 1,9k + 8,8t