Math Problem Statement

solve

At exactly two of the labeled points in the figure below, which shows a function f, the derivative f' is zero; the second derivative f'' is not zero at any of the labeled points. Select the correct signs for each of f, f', and f'' at each marked point A, B, C, D, and E.

Solution

The given problem involves analyzing a graph of a function f(x)f(x) and determining the signs of the function ff, its first derivative ff' (slope), and its second derivative ff'' (concavity) at five labeled points: A, B, C, D, and E.

Steps to solve:

  • f(x)f(x): This indicates whether the function's value is positive, negative, or zero at each point.
  • f(x)f'(x): The slope of the tangent at a point (first derivative) tells if the function is increasing or decreasing.
    • f(x)>0f'(x) > 0: Function is increasing.
    • f(x)<0f'(x) < 0: Function is decreasing.
    • f(x)=0f'(x) = 0: Indicates a critical point, which could be a local max, min, or inflection point.
  • f(x)f''(x): The concavity of the function (second derivative) tells if the function is concave up or concave down.
    • f(x)>0f''(x) > 0: Concave up.
    • f(x)<0f''(x) < 0: Concave down.

Let's analyze each point:

  1. Point A:

    • f(x)<0f(x) < 0 (since it is below the x-axis).
    • f(x)=0f'(x) = 0 (since it is a flat point, likely a local minimum).
    • f(x)>0f''(x) > 0 (since it is concave up).
  2. Point B:

    • f(x)=0f(x) = 0 (on the x-axis).
    • f(x)>0f'(x) > 0 (function is increasing as we move right from B).
    • f(x)>0f''(x) > 0 (since it is still concave up).
  3. Point C:

    • f(x)>0f(x) > 0 (since it is above the x-axis).
    • f(x)=0f'(x) = 0 (since it is a flat point, likely a local maximum).
    • f(x)<0f''(x) < 0 (since it is concave down).
  4. Point D:

    • f(x)>0f(x) > 0 (since it is above the x-axis).
    • f(x)<0f'(x) < 0 (function is decreasing as we move right from D).
    • f(x)<0f''(x) < 0 (concave down).
  5. Point E:

    • f(x)<0f(x) < 0 (since it is below the x-axis).
    • f(x)<0f'(x) < 0 (function is decreasing as we move right from E).
    • f(x)>0f''(x) > 0 (since it is concave up).

Final table of signs:

Pointffff'ff''
A-0+
B0++
C+0-
D+--
E--+

Would you like further explanation on any part of this solution?


Here are some relative questions:

  1. How can the sign of the second derivative influence the shape of the graph?
  2. Why is f(x)=0f'(x) = 0 at local maximum and minimum points?
  3. How would inflection points affect both the first and second derivatives?
  4. Can a point exist where both the first and second derivatives are zero? What does that imply?
  5. How can concavity help in determining the nature of critical points?

Tip: Always check concavity (second derivative) when the first derivative is zero to classify critical points accurately.

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Math Problem Analysis

Mathematical Concepts

Calculus
Derivatives
Critical points
Concavity
Sign analysis

Formulas

f'(x) = 0 at local maxima or minima
f'(x) > 0 for increasing intervals
f'(x) < 0 for decreasing intervals
f''(x) > 0 for concave up
f''(x) < 0 for concave down

Theorems

First Derivative Test
Second Derivative Test

Suitable Grade Level

Grades 11-12