Répondre :
(x-1)²-(x+1)² est de la forme a²-b² qu'on factorise (a-b)(a+b)
a² = (x-1)², a = (x-1)
b² = (x+1)², b = (x+1)
donc: [(a)-(b)][(a)+(b)]
[((x-1)-(x+1)]-[(x-1)+(x+1)]
=(x-1-x-1)-(x-1+x+1)
=x-1-x-1-x+1-x-1
= -2x -2
a² = (x-1)², a = (x-1)
b² = (x+1)², b = (x+1)
donc: [(a)-(b)][(a)+(b)]
[((x-1)-(x+1)]-[(x-1)+(x+1)]
=(x-1-x-1)-(x-1+x+1)
=x-1-x-1-x+1-x-1
= -2x -2