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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

Area Find (i) the net area and (ii) the area of the following regions. Graph the function and indicate the region in question.


The region bounded by y = 6 cos 𝓍 and the 𝓍-axis between 𝓍 = ―π/2 and 𝓍 = Ο€

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Textbook Question

Approximating displacement The velocity of an object is given by the following functions on a specified interval. Approximate the displacement of the object on this interval by subdividing the interval into n subintervals. Use the left endpoint of each subinterval to compute the height of the rectangles.

v = [1 / (2t + 1)] (m/s), for 0 ≀ t ≀ 8 ; n = 4

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Textbook Question

Average value of the derivative Suppose Ζ’ ' is a continuous function for all real numbers. Show that the average value of the derivative on an interval [a, b] is ƒ⁻' = (Ζ’(b) ―ƒ(a))/ (b―a) . Interpret this result in terms of secant lines.

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Textbook Question

Variations on the substitution method Evaluate the following integrals.                                                                                                        

                                                                                                                                                                    

 βˆ« yΒ²/(y + 1)⁴ dy

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Textbook Question

Definite integrals Use geometry (not Riemann sums) to evaluate the following definite integrals. Sketch a graph of the integrand, show the region in question, and interpret your result.


 βˆ«β‚€β΄ Ζ’(𝓍) d𝓍, where Ζ’(𝓍) = {5      if π“ ≀ 2                                                                                                                                                                                     

                      3𝓍 ― 1  if π“ > 2

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Textbook Question

Variations on the substitution method Evaluate the following integrals.                                                                                                        

                                                                                                                                                                    

 βˆ« (eΛ£ ― e⁻ˣ)/ (eΛ£ + e⁻ˣ) d𝓍

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