Aplicăm formulele (a+b)² şi (a-b)².
(2a-1)² - (3a+4)² = (2a)²-2·2a·1+1² - ( (3a)²+2·3a·4+4²) = 4a²-4a+1 - (9a²+24a+16) = 4a²-4a+1 - 9a²-24a-16 = -5a²-28a-15
Sau putem aplica formula a²-b².
(2a-1)² - (3a+4)² = (2a-1 + 3a+4)(2a-1 - 3a-4) = (5a+3)(-5-a)
