(1)=-a(a-1)^2(2)=(x+y^2(x-y)^2(3)=(x+5)^2(x-5)^2(x^2+25)^2(4)=(x-1)^4(5)=(x+3)(x^2-3x+9)(6)=(x-3)(x+1)
-a+2a^2-a^3=-a(a-1)^2
