4. Упростите выражения: 2/3(x − 6y) − 1/3(2x − y); x − (x − (3x − 1)); 5a − (6a − (7a − (8a − 9))); 7(5a + 8) − 11a; 6(c + 1) − 6c − 5; 9x + 3(15 − 8x); 19y + 2(3 − 4y) + 11y.

1. \(\frac{2}{3}(x-6y)-\frac{1}{3}(2x-y)=\frac{2x}{3}-4y-\frac{2x}{3}+\frac{y}{3}=-\frac{11y}{3}\).
2. \(x-(x-(3x-1))=x-(-2x+1)=3x-1\).
3. \(5a-(6a-(7a-(8a-9)))=5a-(7a-9)=9-2a\).
4. \(7(5a+8)-11a=35a+56-11a=24a+56\).
5. \(6(c+1)-6c-5=6c+6-6c-5=1\).
6. \(9x+3(15-8x)=9x+45-24x=45-15x\).
7. \(19y+2(3-4y)+11y=19y+6-8y+11y=22y+6\).

Ответ: −11y/3; 3x−1; 9−2a; 24a+56; 1; 45−15x; 22y+6.