For what values of 𝑐 does the curve 𝑓(𝑥) = 2𝑥^3 + 𝑐𝑥^2 + 2𝑥 have maximum and minimum points?
Show that the minimum and maximum points of every curve in the family of polynomials
𝑓(𝑥) = 2𝑥^3 + 𝑐𝑥^2 + 2𝑥 lie on the curve 𝑦 = 𝑥 − 𝑥^3.
We point out that the function increases for large values of . It is due to the fact that the term increases as increases. Consider the derivative: . In case we consider the equation , we get the following discriminant: . Thus, for , . It means, that for those values of the function increases for all values of . Thus, minimum and maximum points are absent. For we get: , . The function increases for and for . It decreases for . Thus, is a local maximum and is a local minimum. Consider the points of intersection of the functions , . We receive: . As we can see, the equation is the same as the equation . It means that minimum and maximum points can be found from intersection of curves and .
Answer: In case , function has no minimum and maximum points. For , , where , is a local maximum and is a local minimum.
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