Rút gọn các biểu thức sau: 4(x - 2y)(x + y) + 4(x +y)^2 + (x - 2y)^2 - 12xy + 4y^4

Ta có: 4x−2yx+y+4x+y2+x−2y2−12xy+4y4

                   =4x−8yx+y+4x2+2xy+y2+x2−4xy+4y2−12xy+4y2

                   =4xx+y−8yx+y+4x2+8xy+4y2+x2−16xy+8y2

                   =4x2+4xy−8xy−8y2+5x2−8xy+12y2

                   =9x2−12xy+4y2=3x2−2.3x.2y+2y2=3x−2y2