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Ch. 3 - Derivatives
Hass - Thomas' Calculus 15th Edition
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3장, 문제 3.9.29

Approximation Error


In Exercises 29–34, each function f(x) changes value when x changes from x₀ to x₀ + dx. Find


a. the change Δf = f(x₀ + dx) − f(x₀);
b. the value of the estimate df = fʹ(x₀) dx; and
c. the approximation error |Δf − df|.


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f(x) = x² + 2x, x₀ = 1, dx = 0.1

검증된 단계별 안내
1
First, calculate the change in the function, Δf = f(x₀ + dx) − f(x₀). Substitute x₀ = 1 and dx = 0.1 into the function f(x) = x² + 2x to find f(x₀ + dx) and f(x₀).
Evaluate f(x₀ + dx) by substituting x = x₀ + dx = 1 + 0.1 = 1.1 into the function: f(1.1) = (1.1)² + 2(1.1).
Evaluate f(x₀) by substituting x = x₀ = 1 into the function: f(1) = 1² + 2(1).
Calculate the derivative of the function, fʹ(x) = d/dx (x² + 2x). This gives fʹ(x) = 2x + 2. Then, find the estimate df = fʹ(x₀) dx by substituting x₀ = 1 and dx = 0.1.
Finally, compute the approximation error |Δf − df| by taking the absolute value of the difference between the change in the function Δf and the estimate df.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Function Change Δf

The change in a function, Δf, represents the difference in the function's value as the input changes from x₀ to x₀ + dx. It is calculated by evaluating the function at the new point and subtracting the function's value at the original point: Δf = f(x₀ + dx) − f(x₀). This concept helps understand how the function behaves over small intervals.
추천 영상:
가이드 코스
06:35
Changing Geometries

Differential Estimate df

The differential estimate, df, is an approximation of the change in the function using the derivative at a specific point. It is calculated as df = fʹ(x₀) dx, where fʹ(x₀) is the derivative of the function at x₀, and dx is the small change in x. This linear approximation is useful for estimating function changes over small intervals.
추천 영상:
가이드 코스
05:53
Finding Differentials

Approximation Error |Δf − df|

The approximation error, |Δf − df|, measures the difference between the actual change in the function and the estimated change using the derivative. It quantifies the accuracy of the linear approximation provided by the differential. A smaller error indicates a better approximation, highlighting the importance of understanding the behavior of the function and its derivative.
추천 영상:
가이드 코스
04:57
Determining Error and Relative Error