1.(2x+y+1)(2x+y-1)
=[(2x+y)+1][(2x+y)-1]
=(2x+y)²-1
=4x²+4xy+y²-1
2.(x-2)(x+2)-(x+1)(x-3)
=x²-4-(x²-2x-3)
=x²-4-x²+2x+3
=2x-1
3.(ab+1)²-（ab-1)²
=(ab+1+ab-1)(ab+1-ab+1)
=2ab×2
=4ab
4、(2x-y)²-4(x-y)(x+2y)
=4x²-4xy+y²-4(x²+2xy-xy-2y²)
=4x²-4xy+y²-4x²-8xy+4xy+8y²
=9y²-8xy