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It is important to be aware of the disadvantages of using calculators
or other automated mathematics systems. This was covered in lesson 1.4, and would be
excellent to review.
Example Problem:
Analyze the function:
.
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First, restate the function. |
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Next, find the first derivative, so that we can find all of the critical points |
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Set the first derivative equal to zero, factor and solve. These then are our critical points. |
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Now we calculate the second derivative. |
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Again, we set the second derivative equal to zero, factor, and solve. We will need to use the quadratic formula for solving the trinomial. These are our inflection points. |
Now, we will set up a table with these key points as "dividers" of the domain.
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Key
Points and Intervals
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f(x)
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f'(x)
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f''(x)
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Analysis
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-
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+
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-
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Negative, increasing, and
concave down
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(0,0)
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0
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0
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0
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-
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-
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-
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Negative, decreasing, and
concave down
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(.369,-.005)
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-.005
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-
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0
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-
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-
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+
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Negative, decreasing, and
concave up
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(.571,-.0084)
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-.0084
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0
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+
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-
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+
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+
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Negative, increasing, and
concave up
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(.773,-.004)
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-.004
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+
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0
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-
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+
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-
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Negative, increasing, and
concave down
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(1,0)
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0
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0
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0
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+
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+
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+
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Positive, increasing, and
concave up
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Now let us make use of the information in this table to make a rough sketch of the function.
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First, we set up a scale which covers the ordered pairs in our table above. We include scales which allow us to plot the ordered pairs. Please note that the scale for the y-axis is not proportional to the scale of the x-axis. This is so that we can see what is happening on this small scale. |
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We now add points for the zeros of the function. |
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Now we add the other key ordered pairs from the above chart. |
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Now, using the "Analysis" column from the above table, we sketch a curve which follows the slope and concavity specified there. |
| Lastly, we compare this to Maple's version. You can see that our estimate of the shape of the first "hump" was inaccurate. Nevertheless, we have a fairly good idea of the behaviour of the function. |
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