16（a-b)^2-9(a+b)^2
=[4(a-b)+3(a+b)]*[4(a-b)-3(a+b)]
=(7a-b)(a-7b)
3(x-y)^3+12(y-x)
=3(x-y)^3-12(x-y)
=3(x-y)[(x-y)^2-4]
=(x-y)(x-y+2)(x-y-2)