Question

[Chi Từ]

Chứng minh đa thức 

1. x²2+xy+y²2=3(x+y/2)²+(x-y/2)²
2. (x+y)(x²-xy+y²)-(x-y)(x²2+xy+y²)=2y

3. ---

   (x+y)³-(x-y)(x²+xy+y²)=y(3x²+3xy+2y²2)