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5.4 Curve Sketching

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 1: Graph the function f given by and find the relative extrema. 1 st find f (x) and f (x).

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 1 (continued): 2 nd solve f (x) = 0. Thus, x = –3 and x = 1 are critical values.

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 1 (continued): 3 rd use the Second Derivative Test with –3 and 1. Lastly, find the values of f (x) at –3 and 1. So, (–3, 14) is a relative maximum and (1, –18) is a relative minimum.

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 1 (concluded): Then, by calculating and plotting a few more points, we can make a sketch of f (x), as shown below.

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Strategy for Sketching Graphs: a) Derivatives and Domain. Find f (x) and f (x). Note the domain of f. b) Find the y-intercept. c) Find any asymptotes. d)Critical values of f. Find the critical values by solving f (x) = 0 and finding where f (x) does not exist. Find the function values at these points.

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Strategy for Sketching Graphs (continued): e) Increasing and/or decreasing; relative extrema. Substitute each critical value, x0, from step (b) into f (x) and apply the Second Derivative Test. f) Inflection Points. Determine candidates for inflection points by finding where f (x) = 0 or where f (x) does not exist. Find the function values at these points.

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Strategy for Sketching Graphs (concluded): g) Concavity. Use the candidates for inflection points from step (d) to define intervals. Use the relative extrema from step (b) to determine where the graph is concave up and where it is concave down. h) Sketch the graph. Sketch the graph using the information from steps (a) – (e), calculating and plotting extra points as needed.

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 3: Find the relative extrema of the function f given by and sketch the graph. a) Derivatives and Domain. The domain of f is all real numbers.

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 3 (continued): b) Critical values of f. And we have f (–1) = 4 and f (1) = 0.

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 3 (continued): c) Increasing and/or Decreasing; relative extrema. So (–1, 4) is a relative maximum, and f (x) is increasing on (–∞, –1] and decreasing on [–1, 1]. The graph is also concave down at the point (–1, 4). So (1, 0) is a relative minimum, and f (x) is decreasing on [–1, 1] and increasing on [1, ∞). The graph is also concave up at the point (1, 0).

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 3 (continued): d) Inflection Points. And we have f (0) = 2. e) Concavity. From step (c), we can conclude that f is concave down on the interval (–∞, 0) and concave up on (0, ∞).

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 3 (concluded) f) Sketch the graph. Using the points from steps (a) – (e), the graph follows.

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 5: Graph the function f given by List the coordinates of any extreme points and points of inflection. State where the function is increasing or decreasing, as well as where it is concave up or concave down.

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 5 (continued) a) Derivatives and Domain. The domain of f is all real numbers.

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 5 (continued) b) Critical values. Since f (x) is never 0, the only critical value is where f (x) does not exist. Thus, we set its denominator equal to zero. And, we have

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 5 (continued) c) Increasing and/or decreasing; relative extrema. Since f (x) does not exist, the Second Derivative Test fails. Instead, we use the First Derivative Test.

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 5 (continued) c) Increasing and/or decreasing; relative extrema (continued). Selecting 2 and 3 as test values on either side of Since f’(x) is positive on both sides of is not an extremum.

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 5 (continued) d) Inflection points. Since f (x) is never 0, we only need to find where f (x) does not exist. And, since f (x) cannot exist where f (x) does not exist, we know from step (b) that a possible inflection point is ( 1).

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 5 (continued) e) Concavity. Again, using 2 and 3 as test points on either side of Thus, is a point of inflection.

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Slide Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison- Wesley Example 5 (concluded) f) Sketch the graph. Using the information in steps (a) – (e), the graph follows.

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