Ответ
12 - 7х = 20 + х
-7х - х = 20 - 12
-8х = 8
х = -1
2х = 7х - 30
2х - 7х = - 30
-5х = -30
х = -30 : -5
х = 6
4х + 5 = 19 - 3х
4х + 3х = 19 - 5
7х = 14
х = 2
26 + 2х = 20 - х
2х + х = 20 - 26
3х = -6
х = -6 : 3
х = -2
х + 7 = х - 7 (утверждение ложно)
3м - м + 5м = 21
7м = 21
м = 21 : 7
м = 3
-z = -5z
-z + 5z= 0
4z = 0
z = 4 * 0
z = 0
0.4(6x - 7) = 0.5(3x + 7)
2.4x - 2.8 = 1.5x + 3.5
2.4x - 1.5x = 3.5 + 2.8
0.9x = 6.3
x = 6.3 : 0.9
x = 7
Незачто)