2. Доведи тотожність. а) 5х – 11 х = 8 + 2x – 9x — 8 + x; б) 5(2x +y) = 9(x+y) +х — 4у; в) 2c + 6 = 6 — 4(с – 5) + 2(3c - 10).​

a) 5x – 11x = 8 + 2x – 9x – 8 + x

(5 – 11)x = (2 – 9 + 1)x + (8 – 8)

–6x = –6x

б) 5(2x + y) = 9(x + y) + x – 4y

10x + 5y = 9x + 9y + x – 4y

10x + 5y = (9 + 1)x + (9 – 4)y

10x + 5y = 10x + 5y

в) 2c + 6 = 6 – 4(c – 5) + 2(3c – 10)

2c + 6 = 6 – 4c + 20 + 6c – 20

2c + 6 = (–4 + 6)c + (6 + 20 – 20)

2c + 6 = 2c + 6