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Ch. 9 - First-Order Differential Equations
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077당신이 사용하는 게 아니라요?교과서 변경
9장, 문제 9.PE.3

In Exercises 1–22, solve the differential equation.


sec x dy + x cos² y dx = 0

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Rewrite the given differential equation in the form \(M(x,y)\,dx + N(x,y)\,dy = 0\). Here, the equation is \(\sec x \, dy + x \cos^{2} y \, dx = 0\), so rearranged it becomes \(x \cos^{2} y \, dx + \sec x \, dy = 0\).
Check if the differential equation is exact by computing the partial derivatives \(\frac{\partial M}{\partial y}\) and \(\frac{\partial N}{\partial x}\), where \(M = x \cos^{2} y\) and \(N = \sec x\).
If the equation is not exact, look for an integrating factor that depends on either \(x\) or \(y\) to make it exact. This often involves checking if \(\frac{1}{N} (\frac{\partial M}{\partial y} - \frac{\partial N}{\partial x})\) is a function of only one variable.
Once the equation is exact (or made exact), find the potential function \(\Psi(x,y)\) such that \(\frac{\partial \Psi}{\partial x} = M\) and \(\frac{\partial \Psi}{\partial y} = N\) by integrating \(M\) with respect to \(x\) and then determining the function of \(y\).
Write the implicit solution as \(\Psi(x,y) = C\), where \(C\) is a constant, representing the general solution to the differential equation.

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주요 개념

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

Differential Equations

A differential equation relates a function with its derivatives. Solving it means finding the function that satisfies this relationship. In this problem, the equation involves derivatives of y with respect to x, and the goal is to find y as a function of x.
추천 영상:
07:39
Classifying Differential Equations

Separable Equations

A separable differential equation can be written so that all terms involving y are on one side and all terms involving x are on the other. This allows integration of each side independently. Recognizing separability is key to solving equations like the one given.
추천 영상:
06:06
Solving Separable Differential Equations

Integration Techniques

Solving separable equations requires integrating functions of x and y separately. Familiarity with integrating trigonometric functions such as sec x and cos² y is essential. Proper integration leads to an implicit or explicit solution of the differential equation.
추천 영상:
06:18
Integration by Parts for Definite Integrals