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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 5.1.69a

Approximating areas Estimate the area of the region bounded by the graph of Ζ’(𝓍) = xΒ² + 2 and the x-axis on [0, 2] in the following ways.
(a) Divide [0, 2] into n = 4 subintervals and approximate the area of the region using a left Riemann sum. Illustrate the solution geometrically.

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First, divide the interval [0, 2] into 4 equal subintervals. Since the length of the interval is 2, each subinterval will have width \(\Delta x = \frac{2 - 0}{4} = 0.5\).
Identify the left endpoints of each subinterval. These will be \(x_0 = 0\), \(x_1 = 0.5\), \(x_2 = 1.0\), and \(x_3 = 1.5\). Note that the left Riemann sum uses the function values at these points.
Evaluate the function \(f(x) = x^2 + 2\) at each left endpoint: calculate \(f(x_0)\), \(f(x_1)\), \(f(x_2)\), and \(f(x_3)\).
Multiply each function value by the width \(\Delta x\) to find the area of each rectangle: \(f(x_i) \times \Delta x\) for \(i = 0, 1, 2, 3\).
Sum all these rectangle areas to approximate the total area under the curve on [0, 2]: \(\text{Left Riemann Sum} = \sum_{i=0}^{3} f(x_i) \Delta x\). This sum represents the approximate area bounded by the graph and the x-axis.

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Key Concepts

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

Riemann Sums

Riemann sums approximate the area under a curve by dividing the interval into subintervals and summing the areas of rectangles formed using function values at specific points. The left Riemann sum uses the left endpoint of each subinterval to determine the rectangle height, providing an estimate of the integral.
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Introduction to Riemann Sums

Partitioning the Interval

Partitioning involves dividing the interval [0, 2] into equal subintervals, here n = 4, to create smaller segments for approximation. Each subinterval has length Ξ”x = (b - a)/n, which is essential for calculating the width of rectangles in the Riemann sum.
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Interval of Convergence

Function Evaluation at Endpoints

To compute the left Riemann sum, evaluate the function f(x) = xΒ² + 2 at the left endpoints of each subinterval. These values determine the heights of the rectangles, which when multiplied by the subinterval width and summed, approximate the total area under the curve.
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Related Practice
Textbook Question

Zero net area Consider the function Ζ’(𝓍) = 𝓍² ― 4𝓍 .

(a) Graph Ζ’ on the interval 𝓍 β‰₯ 0.

Textbook Question

Working with area functions Consider the function Ζ’ and the points a, b, and c.

(a) Find the area function A (𝓍) = βˆ«β‚Λ£ Ζ’(t) dt using the Fundamental Theorem.

Ζ’(𝓍) = cos 𝓍 ; a = 0 , b = Ο€/2 , c = Ο€

Textbook Question

The velocity in ft/s of an object moving along a line is given by v = Ζ’(t) on the interval 0 ≀ t ≀ 6 (see figure), where t is measured in seconds.


(a) Divide the interval [0,6] into n = 3 subintervals, [0,2] , [2,4] and [4,6]. On each subinterval, assume the object moves at a constant velocity equal to the value of v evaluated at the right endpoint of the subinterval, and use these approximations to estimate the displacement of the object on [0,6] (see part (a) of the figure)                                                                                                             

                                                                                                                                                                                                

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Textbook Question

Sigma notation Evaluate the following expressions.

(a)    10                                                                                                                                                                               

       βˆ‘ ΞΊ                                                                                                                                                                          

       ΞΊ=1                         

Textbook Question

Symmetry properties Suppose βˆ«β‚€β΄ Ζ’(𝓍) d𝓍 = 10 and βˆ«β‚€β΄ g(𝓍) d𝓍 = 20. Furthermore, suppose Ζ’ is an even function and g is an odd function. Evaluate the following integrals.


(e) βˆ«β‚‹β‚‚Β² 3𝓍ƒ(𝓍)d𝓍

Textbook Question

Symmetry properties Suppose βˆ«β‚€β΄ Ζ’(𝓍) d𝓍 = 10 and βˆ«β‚€β΄ g(𝓍) d𝓍 = 20. Furthermore, suppose Ζ’ is an even function and g is an odd function. Evaluate the following integrals.


(a) βˆ«β‚‹β‚„β΄ Ζ’(𝓍) d𝓍