a) 2x - 2y - x2 + 2xy - y2
Ta có:2.(x-y)-(x2-2xy+y2)
=2.(x-y)-(x-y)2
=2.(x-y)-(x-y)(x-y)
=(x-y)[2-(x-y)]
b)x4-2x2
Ta có:x4-2x2
=x2.(x2-2)
=x2.(x2-\(\left(\sqrt{2}\right)^2\))
=x2.(x-\(\sqrt{2}\))(x+\(\sqrt{2}\))
c)x4+4
Ta có:x4+4
=(x2)2+22+2.x2.2-4x2
=(x2+2)2-(2x)2
=(x2+2+2x)(x2+2-2x)