Ex3. In business and economics, the point of diminishing returns occurs when there is a decrease in the marginal output of a production. Marginal output of a production is the first derivative, so point of diminishing returns is the change in the first derivative, thus it is the inflection point. Assume a company estimates that it will sale N(x) units of a product after spending $x thousands on advertising. N(x) = -0.25x4 + 23x3 - 540x2 + 80, 000 where 24