1) a la a treia - 2 ori a ori b + b la a doua - 9
a³-2ab+b²-9=(a³-9)+b²-2ab
a³-9=a³-3a²b+3ab²-b³=a³-9a²+3a×9-9=a³-9a²+27a-9
deci (a³-9)+b²-2ab devine
a³-9a²+27a-9 +b²-2ab=a(a²-9a+27) +b²-9
dar b²-9=(b+3)(b-3)
atunci
a(a²-9a+27) +b²-9=
=a(a²-9a+27) +(b+3)(b-3)
2) a la a patra - b la a patra
a²×a²-b²×b² diferenta de patrate
=(a²-b²)(a²+b²)
=(a-b)(a+b)(a²+b²)
