zuai-logo
zuai-logo
  1. AP Calculus
FlashcardFlashcard
Study GuideStudy GuideQuestion BankQuestion BankGlossaryGlossary

How to find local extrema using the Second Derivative Test?

  1. Find critical points. 2. Compute the second derivative. 3. Evaluate the second derivative at each critical point. 4. Determine if each point is a local max, min, or neither.
Flip to see [answer/question]
Flip to see [answer/question]
Revise later
SpaceTo flip
If confident

All Flashcards

How to find local extrema using the Second Derivative Test?

  1. Find critical points. 2. Compute the second derivative. 3. Evaluate the second derivative at each critical point. 4. Determine if each point is a local max, min, or neither.

Steps to determine concavity of a function.

  1. Find the second derivative, f′′(x)f''(x)f′′(x). 2. Set f′′(x)=0f''(x) = 0f′′(x)=0 and solve for x. 3. Create a sign chart for f′′(x)f''(x)f′′(x). 4. Determine intervals of concave up (f′′(x)>0f''(x) > 0f′′(x)>0) and concave down (f′′(x)<0f''(x) < 0f′′(x)<0).

How to find inflection points?

  1. Find the second derivative, f′′(x)f''(x)f′′(x). 2. Set f′′(x)=0f''(x) = 0f′′(x)=0 and solve for x. 3. Check if the concavity changes at each potential inflection point.

What to do if the Second Derivative Test is inconclusive?

Use the First Derivative Test or analyze the behavior of the function around the critical point.

How to use the second derivative to determine if x=cx = cx=c is a local max?

Find f′(x)f'(x)f′(x), set f′(c)=0f'(c) = 0f′(c)=0 to confirm c is a critical point. Then, find f′′(x)f''(x)f′′(x) and evaluate f′′(c)f''(c)f′′(c). If f′′(c)<0f''(c) < 0f′′(c)<0, then x=cx = cx=c is a local max.

How to use the second derivative to determine if x=cx = cx=c is a local min?

Find f′(x)f'(x)f′(x), set f′(c)=0f'(c) = 0f′(c)=0 to confirm c is a critical point. Then, find f′′(x)f''(x)f′′(x) and evaluate f′′(c)f''(c)f′′(c). If f′′(c)>0f''(c) > 0f′′(c)>0, then x=cx = cx=c is a local min.

How to find the global extremum given one critical point?

If the function is continuous and has only one critical point, and that point is a local extremum, then it's also the global extremum.

How to find critical points for f(x)=4sin(x)f(x) = 4sin(x)f(x)=4sin(x) on 0<x<2π0 < x < 2\pi0<x<2π?

  1. Find f′(x)=4cos(x)f'(x) = 4cos(x)f′(x)=4cos(x). 2. Set 4cos(x)=04cos(x) = 04cos(x)=0. 3. Solve for x, which gives x=π2,3π2x = \frac{\pi}{2}, \frac{3\pi}{2}x=2π​,23π​.

Given f(x)=4sin(x)f(x) = 4sin(x)f(x)=4sin(x) and critical point x=π2x = \frac{\pi}{2}x=2π​, how to determine if it's a local max or min?

  1. Find f′′(x)=−4sin(x)f''(x) = -4sin(x)f′′(x)=−4sin(x). 2. Evaluate f′′(π2)=−4f''(\frac{\pi}{2}) = -4f′′(2π​)=−4. 3. Since f′′(π2)<0f''(\frac{\pi}{2}) < 0f′′(2π​)<0, it's a local max.

How to determine the nature of critical points when f′(x)=247xf'(x) = \frac{247}{x}f′(x)=x247​?

  1. Set f′(x)=0f'(x) = 0f′(x)=0 to find critical points, but there are none. 2. Check where f′(x)f'(x)f′(x) is undefined, which is at x=0x=0x=0. 3. Since f(x)f(x)f(x) is not defined at x=0x=0x=0, there are no local extrema.

How does the graph of f′′(x)f''(x)f′′(x) relate to the graph of f(x)f(x)f(x)?

The graph of f′′(x)f''(x)f′′(x) shows the concavity of f(x)f(x)f(x). Positive f′′(x)f''(x)f′′(x) means f(x)f(x)f(x) is concave up, negative f′′(x)f''(x)f′′(x) means f(x)f(x)f(x) is concave down.

What does an inflection point look like on the graph of f(x)f(x)f(x)?

It's a point where the graph changes concavity, from concave up to concave down or vice versa.

How can you identify local extrema on the graph of f(x)f(x)f(x)?

Local maxima are peaks, and local minima are valleys. The tangent line at these points is horizontal (slope = 0).

If the graph of f′′(x)f''(x)f′′(x) is always positive, what does this tell you about f(x)f(x)f(x)?

f(x)f(x)f(x) is always concave up.

If the graph of f′′(x)f''(x)f′′(x) is always negative, what does this tell you about f(x)f(x)f(x)?

f(x)f(x)f(x) is always concave down.

How can you identify critical points from the graph of f′(x)f'(x)f′(x)?

Critical points occur where f′(x)f'(x)f′(x) intersects the x-axis (i.e., f′(x)=0f'(x) = 0f′(x)=0) or where f′(x)f'(x)f′(x) is undefined.

What does the sign of f′(x)f'(x)f′(x) tell you about the graph of f(x)f(x)f(x)?

If f′(x)>0f'(x) > 0f′(x)>0, f(x)f(x)f(x) is increasing. If f′(x)<0f'(x) < 0f′(x)<0, f(x)f(x)f(x) is decreasing.

How to identify a local max on the graph of f′(x)f'(x)f′(x)?

The graph of f′(x)f'(x)f′(x) crosses the x-axis from positive to negative.

How to identify a local min on the graph of f′(x)f'(x)f′(x)?

The graph of f′(x)f'(x)f′(x) crosses the x-axis from negative to positive.

How to identify inflection points on the graph of f′(x)f'(x)f′(x)?

Inflection points occur where f′(x)f'(x)f′(x) has a local max or min.

What is the formula for the second derivative?

f′′(x)=d2dx2f(x)f''(x) = \frac{d^2}{dx^2}f(x)f′′(x)=dx2d2​f(x)

How to determine critical points?

Solve f′(x)=0f'(x) = 0f′(x)=0 or find where f′(x)f'(x)f′(x) is undefined.

Second Derivative Test: Local Minimum

If f′(c)=0f'(c) = 0f′(c)=0 and f′′(c)>0f''(c) > 0f′′(c)>0, then f(c)f(c)f(c) is a local minimum.

Second Derivative Test: Local Maximum

If f′(c)=0f'(c) = 0f′(c)=0 and f′′(c)<0f''(c) < 0f′′(c)<0, then f(c)f(c)f(c) is a local maximum.

How to find the second derivative of f(x)=23x3−52x2−3xf(x) = \frac{2}{3}x^3-\frac{5}{2}x^2-3xf(x)=32​x3−25​x2−3x?

f′(x)=2x2−5x−3f'(x) = 2x^2 - 5x - 3f′(x)=2x2−5x−3, f′′(x)=4x−5f''(x) = 4x - 5f′′(x)=4x−5

What is the second derivative of f(x)=4sin(x)f(x) = 4sin(x)f(x)=4sin(x)?

f′(x)=4cos(x)f'(x) = 4cos(x)f′(x)=4cos(x), f′′(x)=−4sin(x)f''(x) = -4sin(x)f′′(x)=−4sin(x)

What is the second derivative of f(x)=247ln(x2)f(x) = 247ln(x^2)f(x)=247ln(x2)?

f′(x)=494xf'(x) = \frac{494}{x}f′(x)=x494​, f′′(x)=−494x2f''(x) = -\frac{494}{x^2}f′′(x)=−x2494​

What is the formula to check for concavity?

Check the sign of f′′(x)f''(x)f′′(x).

What is the formula to find inflection points?

Solve f′′(x)=0f''(x) = 0f′′(x)=0 or find where f′′(x)f''(x)f′′(x) is undefined.

What is the formula for the second derivative test?

  1. Find critical points using f′(x)f'(x)f′(x). 2. Plug critical points into f′′(x)f''(x)f′′(x). 3. Determine local min/max based on the sign of f′′(x)f''(x)f′′(x).