Question

cm (x-y)^2+(x-y)(x+y)+ 2xy = 2y^2

Answer 1

Xét VT `=(x-y)^2-(x-y)(x+y)+2xy`

            `=x^2-2xy+y^2-(x^2-y^2)+2xy`

            `=x^2-2xy+y^2-x^2+y^2+2xy`

           `=2y^2`

            `=` VP ( đpcm )

Answer 2

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

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

\(=2x^2\)