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Ch. 4 - Applications of Derivatives
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
Chapter 4, Problem 4.3.62

Identifying Extrema


In Exercises 61 and 62, the graph of f' is given. Assume that f is continuous, and determine the x-values corresponding to local minima and local maxima.


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Examine the graph of f'. The graph shows horizontal lines, indicating constant values of f' over intervals.
Identify the intervals where f' is positive, negative, or zero. Positive values of f' suggest f is increasing, negative values suggest f is decreasing, and zero values suggest potential extrema.
Look for points where f' changes sign. These points are candidates for local extrema. A change from positive to negative indicates a local maximum, while a change from negative to positive indicates a local minimum.
In the graph, f' is positive for x < 0, zero at x = 0, and negative for x > 0. This suggests a local maximum at x = 0.
Verify the continuity of f at the identified points. Since f is continuous, the behavior of f' at these points confirms the presence of local extrema.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Derivative and Critical Points

The derivative of a function, denoted as f', represents the rate of change of the function f. Critical points occur where the derivative is zero or undefined, indicating potential locations for local maxima or minima. Analyzing these points is essential for identifying where the function changes from increasing to decreasing or vice versa.
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Critical Points

First Derivative Test

The First Derivative Test is a method used to determine the nature of critical points. If f' changes from positive to negative at a critical point, it indicates a local maximum; if it changes from negative to positive, it indicates a local minimum. This test helps in classifying the extrema based on the behavior of the derivative around the critical points.
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The First Derivative Test: Finding Local Extrema

Continuity of the Function

Continuity of a function f is crucial for applying the concepts of calculus effectively. A continuous function does not have breaks, jumps, or holes, ensuring that the behavior of f' accurately reflects the behavior of f. This property guarantees that local extrema identified through the derivative correspond to actual extrema in the function itself.
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Intro to Continuity
Related Practice
Textbook Question

Identifying Extrema


In Exercises 61 and 62, the graph of f' is given. Assume that f is continuous, and determine the x-values corresponding to local minima and local maxima.


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Textbook Question

In Exercises 1–10, find the extreme values (absolute and local) of the function over its natural domain, and where they occur.

______

y = √𝓍² ― 1

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Textbook Question

54. Fermat’s principle in optics Light from a source A is reflected by a plane mirror to a receiver at point B, as shown in the accompanying figure. Show that for the light to obey Fermat’s principle, the angle of incidence must equal the angle of reflection, both measured from the line normal to the reflecting surface. (This result can also be derived without calculus. There is a purely geometric argument, which you may prefer.)

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Textbook Question

Identify the inflection points and local maxima and minima of the functions graphed in Exercises 1–8. Identify the open intervals on which the functions are differentiable and the graphs are concave up and concave down.

2. y=x^4/4-2x^2+4

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Textbook Question

Absolute Extrema on Finite Closed Intervals


In Exercises 21–36, find the absolute maximum and minimum values of each function on the given interval. Then graph the function. Identify the points on the graph where the absolute extrema occur, and include their coordinates.


f(t) = 2 − |t|, −1 ≤ t ≤ 3

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Textbook Question

Initial Value Problems


Find the curve y = f(x) in the xy-plane that passes through the point (9,4) and whose slope at each point is 3√x.

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