Generally speaking, the margin is increment (no matter what margin is the same, if it is negative, it is negative, or decreased), and the income increment of 0 means that the income will no longer increase, and of course the income will be maximized. In mathematical language, the margin is the derivative, and the derivative of 0 is the extreme point. \ r \ Marginal income is income increment and marginal profit is profit increment, and there is a cost increment (marginal cost) between them. Namely marginal revenue-marginal cost = marginal profit. When the profit is maximized, the profit no longer increases, that is, the profit increment is 0, that is, the marginal profit is 0. At this time, it can be seen from the above equation that the marginal revenue is equal to the marginal cost. In fact, revenue is what we often call gross income, and profit is net income (income after cost is removed). Every increase in income includes an increase in costs and an increase in profits. \ r \ The key is to know what the profit is. To be exact, the allowance is the amount of change (increase or decrease). For example, the input cost, if the manufacturing product gains income, increasing the cost input will naturally cause income changes. The changed income is marginal income, and the corresponding cost input is marginal cost. \ r \ nI I hope you are satisfied. If you are not clear, you can ask again.