(1) ax^4-81a =a(x^4-81)=a(x²+9)(x²-9)=a(x²+9)(x+3)(x-3)(2) 4x^2(x-y)+2x(x-y)=2x(x-y)(2x+1)(3) a^2x^2+4a^2xy+4a^2y^2=a²(x²+4xy+4y²)=a²(x+2y)²