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2. (a+b)4-(a-b)4=(a4+2*2ab+b4)-(a4-2*2ab+b4)=(a4+4ab+b4)-(a4-4ab+b4)=a(a3+4b+b4)+a(a3+4b+b4)=(a3+4b+b4)(a+a) 1. (x-3y)4-27x+81y=(x4-2*2(x*3y)+(3y)4)-27x+81y=(x4-4(3y)+81y4) -27x+81y=(x4-12y+81y4)-27x+81y = (x4-12y+81y4)-(27x+81y)=(x4-12y+81y4)-9(3x-9y)= =3y(x4-4+27y3)-9(3x-9y)=(3y-9)(x4-4+27y3)(3y-9)=x4-4+27y3