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Ch. 5 - Integration
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Not the one you use?Change textbook
Chapter 5, Problem 5.4.33

Average distance on a parabola What is the average distance between the parabola y = 30𝓍 (20 ― 𝓍 ) and the 𝓍-axis on the interval [0, 20] ?

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Step 1: Recognize that the average distance between the parabola and the x-axis is calculated using the formula for the average value of a function over an interval. The formula is: 1/(b-a)f(x)dx, where [a, b] is the interval and f(x) is the function.
Step 2: Substitute the given parabola equation y = 30𝓍(20 βˆ’ 𝓍) into the formula. Here, f(x) = 30𝓍(20 βˆ’ 𝓍), and the interval is [0, 20]. The formula becomes: 1/(20-0)30(x)dx.
Step 3: Simplify the parabola equation. Expand y = 30𝓍(20 βˆ’ 𝓍) to get y = 600𝓍 βˆ’ 30𝓍². This is the function to integrate over the interval [0, 20].
Step 4: Set up the integral for the average value. The integral becomes: 1/20(600x-30x2)dx, where the limits of integration are 0 and 20.
Step 5: Compute the integral. Break it into two parts: 600xdx and 30x2dx. Evaluate each term separately, apply the limits of integration, and divide the result by 20 to find the average value.

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Key Concepts

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

Average Value of a Function

The average value of a continuous function over an interval [a, b] is calculated using the formula (1/(b-a)) * ∫[a to b] f(x) dx. This concept is essential for determining the average distance between the parabola and the x-axis, as it involves integrating the function that represents the distance from the x-axis over the specified interval.
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Definite Integral

A definite integral computes the accumulation of a quantity, represented as the area under a curve between two points on the x-axis. In this context, the definite integral of the function y = 30x(20 - x) from 0 to 20 will provide the total area under the parabola, which is necessary for finding the average distance to the x-axis.
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Parabola Properties

A parabola is a symmetric curve defined by a quadratic function, which can open upwards or downwards. The given function y = 30x(20 - x) describes a downward-opening parabola with its vertex at the maximum point. Understanding the shape and properties of parabolas is crucial for visualizing the distance from the x-axis and interpreting the results of the integration.
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Related Practice
Textbook Question

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 βˆ«β‚€β΄ (8―2𝓍) d𝓍

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Textbook Question

Indefinite integrals Use a change of variables or Table 5.6 to evaluate the following indefinite integrals. Check your work by differentiating.                                                                                  

                                                                                                                                                                    

 βˆ« sin 𝓍 sec⁸ 𝓍 d𝓍

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Textbook Question

Why can the constant of integration be omitted from the antiderivative when evaluating a definite integral?

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The linear function Ζ’(𝓍) = 3 ― 𝓍 is decreasing on the interval [0, 3]. Is its area function for Ζ’ (with left endpoint 0) increasing or decreasing on the interval [0, 3]? Draw a picture and explain. 

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Variations on the substitution method Evaluate the following integrals.                                                                                                        

                                                                                                                                                                    

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Textbook Question

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