Докажите тождество: 1) 3(7 - a) - 7(1 - 3a) = 14 + 18a 2) (6x - 8) - 5x - (4 - 9x) = 10x -12 3) 3(2.1m - n) - 0,9(7m + 2n) = -4,8n 4)2/3(-3/8х + 6) -1/6(24 - 1 1/2х) = 0

21-3a-7+21a=14+18a
6x-8-5x-4+9x=10x-12
6.3m-n-6.3m-1.8n=-2.8
-1/4x+4-4+11/12x=3/4

1) 3(7-a)-7(1-3a)=14+18a
21-3a-7+21a=14+18
14+18a=14+18a
2) (6x-8)-5x-(4-9x)=10x-12
6x-8-5x-4+9x=10x-12
10x-12=10x-12
3) 3(2.1m-n)-0.9(7m+2n)=-4.8
6.3m-3n-6.3m-1.8n=-4.8n
6.3 и -6.3 сокращаются
-3n-1.8n=-4.8n
4.8n=4.8n