x分之y-y分之x- (xy)分之(x²+y²)
=(xy)分之[y²-x²-（x²+y²)]
=(xy)分之2y²
=x分之2y是-x分之2y把？抱歉，做错了。更正如下：x分之y-y分之x- (xy)分之(x²+y²)=(xy)分之[y²-x²-（x²+y²)]=(xy)分之(-2x²)=-y分之2x