-a+2a²-a^33ax²-3ay²16a²b-16a^3-4ab²x²(y²-1)+(1-y²)

-a+2a²-a^33ax²-3ay²16a²b-16a^3-4ab²x²(y²-1)+(1-y²)
-a+2a²-a^3
3ax²-3ay²
16a²b-16a^3-4ab²
x²(y²-1)+(1-y²)

-a+2a²-a^33ax²-3ay²16a²b-16a^3-4ab²x²(y²-1)+(1-y²)
-a+2a²-a^3=-a(a²-2a+1)=-a(a-1)²
3ax²-3ay²=3a(x²-y²)=3a(x+y)(x-y)
16a²b-16a^3-4ab²=-4a(4a²-4ab+b²)=-4a(2a+b)²
x²(y²-1)+(1-y²)=(y²-1)（x²-1）=(x+1)(y+1)(x-1)(y-1)