1) 0,42x - 9 = 0,12x
0,42x - 0,12x = 9
x(0,42-0,12) = 9
x(42/100 - 12/100) = 9
x * 30/100 = 9
x * 3/10 = 9
x = 9:3/10
x = 9x10/3
x = 30
2) 4x+1,2(3) = 1,9 + 3x
4x-3x = 1,9 - 1,2(3)
x = 19/10 - (123-12)/90 = 19/10- 111/90 = 19/10 - 37/30 = 57/30 - 37/30
x = 20/30
x = 2/3
3) (x+1/2)^2 + (2/3-1/6)^2
x+1/2 = 2/3-1/6
x = 2/3-1/6-1/2 = 4/6-1/6-3/6
x = 0
