Réponses

2013-05-28T20:09:26+02:00
(5x-3)²-81 = (5x-3)²-9²
= (5x-3+9)(5x-3-9)
= (5x+6)(5x-12)
Voila ;)
2013-05-28T20:09:49+02:00

Factoriser 

Tu entoure (5x-3)

et tu ecrit :

(5x-3) (5x-3-81)

(5x-3) (-79x)

Voila