Réponses

2013-02-25T19:23:18+01:00

= n²+2n+1 - ( n²-2n+1)

= n²+2n+1 - n²+2n -1

=4n

2013-02-25T19:29:02+01:00

Bonsoir

(n+1)² - (n-1)²  est de la forme a²-b² =(a-b)(a+b) 

(n+1 - n+1)(n+1+n-1) 

(2)( 2n ) = 4n