a²b-ab²+b²c-bc²+c²a-ca²=(a²b-ca²)-a(b²-c²)+bc(b-c)=a²(b-c)-a(b+c)(b-c)+bc(b-c)=(b-c)[a²-a(b+c)+bc]=(b-c)(a²-ab-ac+bc)=(b-c)[a(a-b)-c(a-...