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Ch. 9 - Differential Equations
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243당신이 사용하는 게 아니라요?교과서 변경
9장, 문제 9.2.36b

33–36. {Use of Tech} Computing Euler approximations Use a calculator or computer program to carry out the following steps.
b. Using the exact solution (also given), find the error in the approximation to y(T) (only at the right endpoint of the time interval).


y′(t) = t/y, y(0) = 4; Δt = 0.1, T = 2; y(t) = √(t² + 16)

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1
Identify the given differential equation and initial condition: \(y'(t) = \frac{t}{y}\) with \(y(0) = 4\).
Note the exact solution provided: \(y(t) = \sqrt{t^2 + 16}\), which will be used to find the error at \(T = 2\).
Use Euler's method with step size \(\Delta t = 0.1\) to approximate \(y(2)\). Recall Euler's formula: \(y_{n+1} = y_n + \Delta t \cdot f(t_n, y_n)\), where \(f(t, y) = \frac{t}{y}\).
Starting from \(t_0 = 0\) and \(y_0 = 4\), iteratively compute \(y_1, y_2, \ldots, y_{20}\) (since \(\frac{2}{0.1} = 20\) steps) using Euler's method.
Calculate the error at \(t = 2\) by subtracting the Euler approximation \(y_{20}\) from the exact solution \(y(2) = \sqrt{2^2 + 16}\): \(\text{Error} = |y(2) - y_{20}|\).

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주요 개념

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

Euler's Method

Euler's Method is a numerical technique to approximate solutions of first-order differential equations. It uses a step size Δt to iteratively estimate the value of the function at discrete points, starting from an initial condition. The method updates the solution by adding the product of the derivative and the step size to the previous value.
추천 영상:
07:33
Euler's Method

Exact Solution of Differential Equations

The exact solution is an explicit formula that satisfies the differential equation and initial conditions. In this problem, y(t) = √(t² + 16) is the exact solution, providing the true value of y at any time t. Comparing the exact solution to numerical approximations helps assess accuracy.
추천 영상:
04:00
Solutions to Basic Differential Equations

Error Analysis in Numerical Methods

Error analysis involves calculating the difference between the numerical approximation and the exact solution at a specific point, here at t = T. This error quantifies the accuracy of the approximation and helps in understanding how step size and method choice affect results.
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04:57
Determining Error and Relative Error
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교과서 질문

29–32. {Use of Tech} Errors in Euler’s method Consider the following initial value problems.


b. Using the exact solution given, compute the errors in the Euler approximations at t=0.2 and t=0.4.


y′(t) = −y, y(0) = 1; y(t) = e⁻ᵗ

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교과서 질문

{Use of Tech} Intravenous drug dosing The amount of drug in the blood of a patient (in milligrams) administered via an intravenous line is governed by the initial value problem y’(t) = -0.02y + 3, y(0) = 0 where t is measured in hours.


b. What is the steady-state level of the drug?

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교과서 질문

Explain why or why not Determine whether the following statements are true and give an explanation or counterexample


b. If k>0 and b>0 then y(t)=0 is never a solution of y'(t)=ky−b.

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교과서 질문

Explain why or why not Determine whether the following statements are true and give an explanation or counterexample.

b. The general solution of the separable equation y'(t) = t/(y' + 10y⁴) can be expressed explicitly with y in terms of t.

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교과서 질문

52-56. In this section, several models are presented and the solution of the associated differential equation is given. Later in the chapter, we present methods for solving these differential equations.


{Use of Tech} Tumor growth The growth of cancer tumors may be modeled by the Gompertz growth equation. Let M(t) be the mass of a tumor, for t ≥ 0. The relevant initial value problem is:


dM/dt = -rM(t)ln(M(t)/K), M(0) = M₀,


where r and K are positive constants and 0 < M₀ < K.


b. Graph the solution for M₀ = 100 and r = 0.05.

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23–26. Stirred tank reactions For each of the following stirred tank reactions, carry out the following analysis.

b. Solve the initial value problem.


A 500-L tank is initially filled with pure water. A copper sulfate solution with a concentration of 20 g/L flows into the tank at a rate of 4 L/min. The thoroughly mixed solution is drained from the tank at a rate of 4 L/min.

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