Both Extremes Inside

Problem

The function

f(x)=13x3+12bx2+cx+df(x) = \frac13 x^3 + \frac12 b x^2 + cx + d

has both a local maximum and a local minimum in the interval (0,1)(0, 1). Find the range of

c2+(1+b)c.c^2 + (1+b)c.

Answer

Solution

Difficulty6/10
TopicsQuadratic Equations, Extrema, calculus, AM-GM, Vieta's Formulas

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