请参考：设一开始加入xkg糖（x > 0）,那么糖水的浓度为x/(x + 1) ；若再添加ykg糖（y > 0）,那么此时糖水的浓度为(x + y)/(x +y + 1),作差可得(x + y)/(x +y + 1) – x/(x + 1) = [(x + y)(x + 1) – x(x + y + 1)]/...