x^3-x=x(x^2-1)=x(x+1)(x-1)3ax^2-6axy+3ay^2=3a(x^2-2xy+y^2)=3a(x-y)^23a^2-27b^2=3(a^2-9b^2)=3(a+3b)(a-3b)8(a-b)²-12(b-a) =8(a-b)^2+12(a-b)=4(a-b)(2a-2b+3a-3b)=4(a-b)(5a-5b)=20(a-b)^2