(a²-ac²+2c²-4)/(a²+2a+2c²-c^4)=[(a²-4)-(ac²-2c²)]/[(a²-c^4)+(2a+2c²)]=
=[(a-2)(a+2)-c²(a-2)]/(a-c²)(a+c²)+2(a+c²)]=(a-2)(a+2-c²)/[(a+c²)(a-c²+2)]=
=(a-2)/(a+c²)
(a²-4a+4)/(a²+ac²-2a-2c²)=(a-2)²/[a(a-2)+c²(a-2)]=(a-2)²/[(a-2)(a+c²)]=
=(a-2)/(a+c²)
(a-2)/(a+c²)-(a-2)/(a+c²)=0