Math 110 Course Resources - Curve Sketching Course Packet on points of diminishing & increasing returns The total monthly revenue R(x) generated from sales of Calculus videos is related to the amount x spent on advertising by R(x)= -8x3 + 120x2 + 80x + 40 where x is in thousands of dollars. Calculate the point of diminishing returns for advertising costs. The point of diminishing returns occurs at X = 5 . This means that if more than x dollars is spent on advertising, then each additional dollar spent produces a larger x return on investment than the previous dollar