1.(2x+y+1)(2x+y-1)2.(x-2)(x+2)-(x+1)(x-3)3.(ab+1)平方-（ab-1)平方4.（2x-y)平方-4（x-y)(x+2y)

Question

1.(2x+y+1)(2x+y-1)
2.(x-2)(x+2)-(x+1)(x-3)
3.(ab+1)平方-（ab-1)平方
4.（2x-y)平方-4（x-y)(x+2y)

Answer 1

1.(2x+y+1)(2x+y-1)=(2x+y)^2-1=4x^2+4xy+y^2-1
2.(x-2)(x+2)-(x+1)(x-3)=x^2-4-(x^2-2x-3)=x^2-4-x^2+2x+3=2x-1
3.(ab+1)平方-（ab-1)平方=(ab+1+ab-1)(ab+1-ab+1)=4ab
4.（2x-y)平方-4（x-y)(x+2y)=4x^2-4xy+y^2-4(x^2+2xy-xy-2y^2)=4x^2-4xy+y^2-4x^2-4xy+2y^2
=3y^2-8xy