One or more options correct
Let . Which of the following is/are correct?
- A. has a local maximum at , a local minimum at , and no other local extremum
- B.
- C. The graph of has exactly three points of inflection
- D. The equation has three distinct real roots
Show answer and solution
Answer: A, C
We have . The sign is for , on (the square factor does not change it at ), and for . So has a local maximum at , a local minimum at , and is only a stationary point; (A) is true. Expanding, , giving and , so and (B) is false. Next has three simple roots , each a sign change, so there are three inflection points and (C) is true. Since , is increasing up to a positive local maximum and stays positive afterwards, and the quintic's other roots are complex, so has only one real root and (D) is false.
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