Question

thực hiện phép tính : ( x + y + 1 ) * ( x + y - 1 ) - ( x - y )^2 - 4xy 

Answer 1

Ta có: \(\left(x+y+1\right)\left(x+y-1\right)-\left(x-y\right)^2-4xy\)

\(=\left(x+y\right)^2-\left(x-y\right)^2-1-4xy\)

\(=x^2+2xy+y^2-x^2+2xy-y^2-1-4xy\)

=-1

Answer 2

`(x+y+1)(x+y-1)-(x-y)^{2}-4xy`

`=(x+y)^{2}-1-(x-y)^{2}-4xy`

`=(x+y+x-y)(x+y-x+y)-1-4xy`

`=2x.2y-4xy-1`

`=4xy-4xy-1`

`=-1`