mx²-16my²
=m(x²-16y²)
=m(x-4y)(x+4y)
-2a³+12a²-18a
=-2a(a²-6a+9)
=-2a(a-3)²
4+12(x-y)+9(x-y)²
=[2+3(x-y)]²
=(2+3x-3y)²