$a, 16x^4(x-y)-x+y$
$=16x^4(x-y)-(x-y)$
$=(16x^4-1)(x-y)$
$=[(4x²)²-1²](x-y)$
$=(4x²-1)(4x²+1)(x-y)$
$=[(2x)²-1²](4x²+1)(x-y)$
$=(2x-1)(2x+1)(4x²+1)(x-y)$
$b,2x³y-2xy³-4xy²-2xy$
$=2xy(x²-y²-2y-1)$
$=2xy[x²-(y²+2y.1+1)]$
$=2xy[x²-(y+1)²]$
$=2xy(x-y-1)(x+y+1)$