3) a) a + (a-10) - (12+a) = a + a - 10 - 12 - a = (1+1-1)a - 22 = a - 22
Ответ: $$a - 22$$
б) (6x - 8) - 5x - (4 - 9x) = 6x - 8 - 5x - 4 + 9x = (6-5+9)x + (-8-4) = 10x - 12
Ответ: $$10x - 12$$