29. If f is a function such that f' > 0 for a < x < c, f'' < 0 for a < x < b, and f'' > 0 for b < x < c, which of the following could be the graph of f?






Answer is: option3

(C)

Solution:

\( f'(x) > 0 \) for \( a < x < c \)

→ The function is increasing on the entire interval from \( a \) to \( c \)

\( f''(x) < 0 \) for \( a < x < b \)

→ The function is concave down from \( a \) to \( b \)

\( f''(x) > 0 \) for \( b < x < c \)

→ The function is concave up from \( b \) to \( c \)

We are looking for a graph that is:

  1. Increasing from \( a \) to \( c \)
  2. Concave down from \( a \) to \( b \)
  3. Concave up from \( b \) to \( c \)

Option A:

  • Increasing: Yes
  • Concave up from \( a \) to \( b \): No (should be concave down)
  • Concave down from \( b \) to \( c \): No (should be concave up)

→ Does not match.

Option B:

  • Decreasing from \( a \) to \( c \): No (violates \( f' > 0 \))

→ Does not match.

Option C:

  • Increasing: Yes
  • Concave down from \( a \) to \( b \): Yes
  • Concave up from \( b \) to \( c \): Yes

→ Matches all conditions.

Option D:

  • Decreasing from \( a \) to \( c \): No (violates \( f' > 0 \))

→ Does not match.

Final Answer: Option C

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