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Worksheets›Calculus›Applications of derivatives›Critical points, extrema and increasing intervals

Critical Points, Extrema and Increasing Intervals Worksheets

Free printable worksheets with answer keys. Pick a level, preview the questions, then open the sheet to swap or delete any single question.

CalculusAnswer key includedPDF · Print
Open in generatorStart with an easy sheet

Easy: Critical points

  1. 1.f(x) = −x3 + 48x + 3Find the critical points.
  2. 2.f(x) = x3 − 9x2 + 15x − 6Find the critical points.
  3. 3.f(x) = −x3 + 3xFind the critical points.
  4. 4.f(x) = 3x3 + 452x2 + 36x + 4Find the critical points.
  5. 5.f(x) = 2x3 − 27x2 + 120x − 6Find the critical points.
  6. 6.f(x) = −x3 − 152x2 − 12x + 7Find the critical points.
Preview shows 6 of 12 questions. Every sheet is new; open it to change any question.

Worksheet variations

Critical points are where f′(x) = 0 (or doesn't exist). Between them f′ keeps one sign: where f′ > 0 the function increases, where f′ < 0 it decreases. A critical point where f′ changes from + to − is a local maximum; from − to + it is a local minimum.

Easyf(x) = −2x3 + 12x2 + 6Find the critical points.Critical pointsMediumf(x) = 2x3 − 6x2 − 90x + 6Find where f has a local maximum and a local minimum.Local maxima and minimaHardf(x) = −2x3 + 6x − 1Find where f is increasing and where it is decreasing.Increasing and decreasing intervals

How to solve it: a worked example

Use the first derivative to answer each question.

  1. Startf(x) = 3x3 + 18x2 + 27x + 3Find the critical points.
  2. Differentiatef′(x) = 9x2 + 36x + 27 = 9(x + 3)(x + 1)
  3. Set f′(x) = 0x = −3, x = −1
  4. Answerx = −1 or x = −3

Common mistakes to watch for

  • Setting f(x) = 0 instead of f′(x) = 0.
  • Mixing up which sign change gives a maximum.
  • Giving the y-value when the question asks where the extremum is.

Tip: tick “Step-by-step answer key” in the generator to print each step for marking.

Related worksheets

Position, velocity and accelerationOptimization problemsRelated ratesConcavity and inflection pointsLimits by direct substitution

FAQ

Is every critical point a maximum or minimum?

No. f′ must change sign there. f(x) = x³ has a critical point at 0, but f′ is positive on both sides, so it's neither.

How does the second derivative test work?

At a critical point, f″ > 0 means the graph is concave up, so it's a local minimum; f″ < 0 means a local maximum. If f″ = 0 the test is inconclusive.

Is every worksheet different?

Yes. Numbers are generated each time, and the answer key is calculated for that sheet. Swap any single question and its answer updates too.

Can I mix critical points, extrema and increasing intervals with other skills?

Yes. In the generator, add more skills; each gets its own section on the sheet with its own instructions.

Is it free to print?

Yes. Generating and printing from the browser is free with no sign-up. PDF downloads need a free account.