докажите тождество:
1) -0,2(4b - 9) + 1.4b = 0.6b + 1.8
2) (5a -3b) - (4 + 5a - 3b) = -4
3)5(0.4x - 0.3) + (0.8 - 0.6x) = 1.4x - 0.7
4) 1/9 (3y - 27) - 2 (1/12y - 1.5) = 1/6y