a)

2x + x – 3 – 4x = 5x + 9

–x – 3 = 5x + 9

–x – 5x = 9 + 3

–6x = 12     / : (–6)       dzielimy obustronnie przez –6

x = –2

Sprawdzenie:

L = 2x + x – 3 – 4x = 2 · (-2) + (–2) – 3 – 4 · (–2) = –4 – 2 – 3 + 8 = –1

P = 5x + 9 = 5 · (–2) + 9 = –10 + 9 = –