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Finding the Area of a Region In Exercises \(31-36,\) (a) use a graphing utility to graph the region bounded by the graphs of the equations, (b) find the area of the region analytically, and (c) use the integration capabilities of the graphing utility to verify your results. $$ f(x)=x^{4}-9 x^{2}, \quad g(x)=x^{3}-9 x $$

Short Answer

Expert verified
This task requires graphing both functions, finding their points of intersection, and calculating the area between them using integration. Once achieved, verify these results using the integration capabilities of the graphing utility.

Step by step solution

01

Graphing the Functions

Start by plotting the functions \(f(x) = x^{4}-9x^{2}\) and \(g(x) = x^{3}-9x\) on graph paper or using a graphing utility. The area in question lies between these two curves.
02

Finding Points of Intersection

The points of intersection of the two equations are the solutions to the equation \(f(x) = g(x)\), which translates to \(x^{4}-9x^{2} = x^{3}-9x\). Solve this to get the x-values.
03

Analytical Approach to Find the Area

After finding the two points of intersection you can calculate the area of the region by integrating from the smaller x-value to the larger x-value and finding the absolute difference between \(f(x)\) and \(g(x)\). In mathematical form: \(\int_{a}^{b}|f(x) - g(x)| dx\), where a and b are the x-values found in the previous step.
04

Using Graphing Utility to Verify the Results

Most graphing utilities come equipped with functions to perform integrals. Use this functionality to integrate the absolute difference between the two functions over the interval determined in step 2. This should verify the results obtained in the previous step.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Graphing Functions
When faced with the challenge of finding the area between two curves, one of the first and most crucial steps is to graph the functions. Graphing functions serves multiple purposes: it provides a visual representation of the functions themselves, it helps to identify the region whose area we are interested in, and it assists in finding the points of intersection between the functions.

In the context of our exercise, graphing the functions \(f(x) = x^{4}-9x^{2}\) and \(g(x) = x^{3}-9x\) allows us to visually capture the shape and behavior of the curves. Typically, we look for where the curves cross each other as well as the behavior at the endpoints to understand the bounds of our area of interest. Utilizing a graphing utility can simplify this step, enabling you to quickly see intersections and estimate regions.
Points of Intersection
To elaborate on the points of intersection, these are the x-values where the two curves meet. They are pivotal in our quest to determine the area between the curves, as they define the limits of integration.

Discovering these points analytically involves setting the two functions equal to each other, \(f(x) = g(x)\), and solving for x. This solution will yield the critical x-values. In our specific problem, solving \(x^{4}-9x^{2} = x^{3}-9x\) will provide us with the intersection points. Understanding the significance of these points and solving for them correctly is integral to the success of finding the area accurately.
Definite Integrals
The concept of the definite integral is at the heart of finding the area between two curves. A definite integral calculates the accumulation of quantities, which in our case, translates to the area under a curve. When we have two curves, the area between them is essentially the difference in their respective areas over the same interval.

Mathematically, this area can be expressed as \[\int_{a}^{b}|f(x) - g(x)| dx\], with 'a' and 'b' being the points of intersection. Why the absolute value? The absolute difference ensures that we always subtract the lower function from the upper function, regardless of which function is on top visually on the graph. Understanding how to set up and evaluate a definite integral is key to finding the correct area.
Integration Techniques
Dealing with integration, especially in the context of finding areas between curves, often requires a strong grasp of various integration techniques. These techniques can include substitution, integration by parts, trigonometric integration, and sometimes numerical integration methods, among others.

In our exercise, the integration may not be straightforward due to the absolute value and the polynomial nature of the functions. It's essential to decide whether to split the integral into sections or to use another technique to simplify the problem. Familiarity with integration techniques will assuredly impact the ease and swiftness with which one can find the area between the curves, reinforcing the importance of this concept in calculus.

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Most popular questions from this chapter

Using a Sphere Find the area of the zone of a sphere formed by revolving the graph of \(y=\sqrt{9-x^{2}}, 0 \leq x \leq 2\)about the \(y\) -axis.

Hydraulic Press In Exercises \(39-42,\) use the integration capabilities of a graphing utility to approximate the work done by a press in a manufacturing process. A model for the variable force \(F\) (in pounds) and the distance \(x\) (in feet) the press moves is given. $$ \text{Force} \quad \text{Interval} $$ $$ F(x)=\frac{e^{x^{2}}-1}{100} \quad 0 \leq x \leq 4 $$

Think About It Consider the equation \(\frac{x^{2}}{9}+\frac{y^{2}}{4}=1\) (a) Use a graphing utility to graph the equation. (b) Set up the definite integral for finding the first-quadrant arc length of the graph in part (a). (c) Compare the interval of integration in part (b) and the domain of the integrand. Is it possible to evaluate the definite integral? Is it possible to use Simpson's Rule to evaluate the definite integral? Explain. (You will learn how to evaluate this type of integral in Section \(8.8 . )\)

Pumping Gasoline In Exercises 23 and \(24,\) find the work done in pumping gasoline that weighs 42 pounds per cubic foot. (Hint: Evaluate one integral by a geometric formula and the other by observing that the integrand is an odd function.) The top of a cylindrical gasoline storage tank at a service station is 4 feet below ground level. The axis of the tank is horizontal and its diameter and length are 5 feet and 12 feet, respectively. Find the work done in pumping the entire contents of the full tank to a height of 3 feet above ground level.

Boyle's Law In Exercises 37 and 38 , find the work done by the gas for the given volume and pressure. Assume that the pressure is inversely proportional to the volume. (See Example \(6 . )\) A quantity of gas with an initial volume of 2 cubic feet and a pressure of 1000 pounds per square foot expands to a volume of 3 cubic feet.

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