3ax²-3ay四次方
=3a(x²-y^4)
=3a(x-y²)(x+y²)
x²(2x-5)+4(5-2x)
=(2x-5)(x²-4)
=(2x-5)(x-2)(x+2)
x³-4xy²
=x(x²-4y²)
=x(x-2y)(x+2y)