z=x³+y³-3xy(x-y)∂z/∂x=3x²-3y(x-y)-3xy=3x²-6xy+3y²∂z/∂y=3y²-3x(x-y)+3xy=3y²+6xy-3x²∂²z/∂x²=6x-6y∂²z/∂x∂y=6y+6x∂²z/∂y²=6x-6y
