Question

[Crazy 2002]

rut gon bieu thuc

a/ (x+y)(x²-xy+y²)-(x-y)(x²+xy+y²)

b/ (x-y)²+ (x+y)²

Answer 1

[Trần Đức Thắng]

a) ( x + y)( x^2 - xy+  y^2 )- ( x - y)( x^2 + xy + y^2 )

= x^3 +y^3 - ( x^3 - y^3 )

= x^3 + y^3 - x^3 + y^3 

= 2y^3 

b; ( x - y)^2 + ( x + y)^2

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

= 2x^2 + 2y^2