1、
=4x²-4xy+y²-4x²-4xy+8y²
=-8xy+9y²
2、
=[x+(y-z)][x-(y-z)]
=x²-(y-z)²
=x²-y²+2yz-z²
3、
=[(2x+y)-z]²
=(2x+y)²-2(2x+y)z+z²
=4x²+4xy+y²-4x-2y+z²