10.
1) 2x = 18 - x
2x + x = 18
3x = 18
x = 18 / 3
x = 6
2) 7x + 3 = 30 - 2x
7x + 2x = 30 - 3
9x = 27
x = 27 / 9
x = 3
3) 7 - 2x = 3x - 18
-2x - 3x = -18 - 7
-5x = -25
5x = 25
x = 25 / 5
x = 5
11.
1) 3(x - 2) = x + 2
3x - 6 = x + 2
3x - x = 2 + 6
2x = 8
x = 8 / 2
x = 4
2) 5 - 2(x - 1) = 4 - x
5 - 2x + 2 = 4 - x
-2x + x = 4 - 5 - 2
-x = -11
x = 11
3) (7x - 1) - (9x + 3) = 5
7x - 1 - 9x - 3 = 5
7x - 9x = 5 + 1 + 3
-2x = 9
-x = 9 / 2
-x = 4.5
x = -4.5
12.
1) 3x + 6 = 2(2x - 7) - x
3x + 6 = 4x - 14 - x
3x - 4x + x = - 14 - 6
0x ≠ -20
x = -20/0
x = ∅
2) 6,2(3 - 2x) = 20 - (12,4x + 1,4)
18,6 - 12,4x = 20 - 12,4x - 1,4
-12,4x + 12,4x = 20 - 1,4 - 18,6
0 = 0
x = R
