(2x-3y)²-4z²
=【（2x-3y)+2z][(2x-3y)-2z]
=(2x-3y+2z)(2x-3y-2z)
x²-y²-2y-1
=x²-(y²+2y+1)
=x²-(y+1)²
=(x+y+1)(x-y-1)