Point of Diminshing Returns ????

[Help Me Please]

I have a problem with many different steps in it. One question asks me to find the x value of the point of diminishing returns, and then the following question asks me to find the point of diminishing returns. I have found the x value for the diminishing returns but is the following question asking the exact same thing??? I am confused on what it is asking.

:?

 

[stapel]

Please provide the exact text of the exercise.

Thank you.

Eliz.

 

[Help Me Please]

A company estimates that it will sell N(x) items after spending $x thousand on advertising, as given by N(x) = 2,000+2x^3+60x^2+450x, where x is greater than or equal to 5 and less than or equal to 15.

it asks to find the rate of change, intervals where it is increasing and decreasing, the maximum rate of change, and the x value of the point of diminishing returns, i have found all of the answers to these...

the following question is to find the point of diminishing returns...thats where i am confused

 

[pka]

A point of diminishing returns is found by finding where the second derivative is zero. That is what is called a point of inflection, the point at which the rate of the rate change is zero.
Find where N"(x)=0.