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Ch. 3 - Derivatives
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077당신이 사용하는 게 아니라요?교과서 변경
3장, 문제 3.9.38

Differential Estimates of Change


In Exercises 35–40, write a differential formula that estimates the given change in volume or surface area.


The change in the lateral surface area S = πr√(r² + h²) of a right circular cone when the radius changes from r₀ to r₀ + dr and the height does not change

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1
Identify the formula for the lateral surface area of a right circular cone: \( S = \pi r \sqrt{r^2 + h^2} \).
Recognize that the problem asks for the change in the lateral surface area when the radius changes from \( r_0 \) to \( r_0 + dr \), while the height \( h \) remains constant.
To estimate the change in \( S \), use the concept of differentials. The differential \( dS \) is given by the derivative of \( S \) with respect to \( r \), multiplied by \( dr \).
Calculate the derivative \( \frac{dS}{dr} \) using the product rule and chain rule: \( \frac{dS}{dr} = \pi \left( \sqrt{r^2 + h^2} + \frac{r^2}{\sqrt{r^2 + h^2}} \right) \).
The differential formula that estimates the change in the lateral surface area is \( dS = \pi \left( \sqrt{r^2 + h^2} + \frac{r^2}{\sqrt{r^2 + h^2}} \right) dr \).

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주요 개념

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Differential Calculus

Differential calculus focuses on the concept of the derivative, which represents the rate of change of a function. In this context, it is used to estimate how small changes in the radius of a cone affect its lateral surface area, assuming the height remains constant.
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06:11
Fundamental Theorem of Calculus Part 1

Lateral Surface Area of a Cone

The lateral surface area of a right circular cone is given by the formula S = πr√(r² + h²), where r is the radius and h is the height. Understanding this formula is crucial for determining how changes in the radius impact the surface area when the height is fixed.
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09:07
Example 1: Minimizing Surface Area

Differential Formula

A differential formula is used to approximate the change in a function's value due to small changes in its variables. For the cone's surface area, the differential formula involves calculating the derivative of the surface area with respect to the radius, providing an estimate of the change when the radius increases by a small amount dr.
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가이드 코스
05:53
Finding Differentials