12.1
1) +1
2)y+2x+6
3)3ab+9
4)23,8 +
12.2
1)41-89
2)85+29mn
3)21b+7
4)13,2kt+2,2z
13.2
1)27x+13y
2)9b-5a
3)-0,5m-7,2n
4)1,9k+8,8t
5) a - 9b
6) a +113d -
Объяснение:
12.3
1)(4x+8y)+(23x+5y) = 4x+8y+23x+5y = 27x+13y
2) (83a-91b) - (89a-100b) = 83a-91b-89a+100b = -5a+9b = 9b-5a
3) (1,5m - 4,2n) - (2m+3n) = 1,5m - 4,2n - 2m - 3n = -0,5m-7,2n
4) (5k+6t)+(2,8t-3,1k) = 5k+6t+2,8t-3,1k = 1,9k+8,8t
5) = = a - 9b
6) = a +113d -
12.1
1)
+1
2)y+2x+6
3)3ab+9
4)23,8
+ 
12.2
1)41-89
2)85+29mn
3)21b+7
4)13,2kt+2,2z
13.2
1)27x+13y
2)9b-5a
3)-0,5m-7,2n
4)1,9k+8,8t
5)
a - 9b
6)
a +113d - 
Объяснение:
12.3
1)(4x+8y)+(23x+5y) = 4x+8y+23x+5y = 27x+13y
2) (83a-91b) - (89a-100b) = 83a-91b-89a+100b = -5a+9b = 9b-5a
3) (1,5m - 4,2n) - (2m+3n) = 1,5m - 4,2n - 2m - 3n = -0,5m-7,2n
4) (5k+6t)+(2,8t-3,1k) = 5k+6t+2,8t-3,1k = 1,9k+8,8t
5)
= 
= 
a - 9b
6)
= 
a +113d - 