Đáp án:
`(x+y)(y+z)(z+x) - 2xyz = = xz^2 + y^2z + yz^2 + x^2y + x^2z + xy^2`
Giải thích các bước giải:
`(x+y)(y+z)(z+x) - 2xyz`
` = (x . y + x . z + y . y + y . z) (z+x) - 2xyz`
` = (xy + xz + y^2 + yz)(z+x) - 2xyz`
` = (xy . z + xz . z + y^2 . z + yz . z + xy . x + xz . x + y^2 . x + yz . x) - 2xyz`
` = (xyz + xz^2 + y^2z + yz^2 + x^2y + x^2z + xy^2 + xyz) - 2xy`
` = xyz + xz^2 + y^2z + yz^2 + x^2y + x^2z + xy^2 + xyz - 2xy`
` = (xyz + xyz - 2xyz) + xz^2 + y^2z + yz^2 + x^2y + x^2z + xy^2`
` = xz^2 + y^2z + yz^2 + x^2y + x^2z + xy^2`
