4x3y - 4xy3 - 8xy2 - 4xy
= 4xy.(x2 - y2 - 2y - 1)
= 4xy.[(x2 - 1) - (y2 + 2y)]
= 4xy.[(x+1).(x-1) - y.(y+2)]
4x3y - 4xy3 - 8xy2 - 4xy = 4xy(x2 - y2 - 2y - 1) = 4xy[x2 - (y2 + 2y1+ 12) = 4xy[x2 - (y-1)2 = 4xy{[x - (y-1)] [x + (y-1)]} = 4xy {[x-y+1][x+y-1]}
