Réponses

2012-09-16T14:06:28+02:00

[(x-y)-(x-z)]-[(z-y)-(x+z)]

= (x-y-x+z)-(z-y-x-z)

= (-y+z)-(-y-x)

= -y+z+y+x

= x + z

 

En espérant t'avoir aidé.

2012-09-16T14:17:32+02:00

Il faut faire : (x-y-x+z)-(z-y-x-z) = (x-y-x+z) - (z-y-x-z) = (-y+z)-(-y-x) = z+x