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Ch. 4 - Applications of Derivatives
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
Chapter 4, Problem 4.7.79

Initial Value Problems


Solve the initial value problems in Exercises 71–90.


dr/dθ = −π sin (πθ), r(0) = 0

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1
Identify the given differential equation and initial condition: \( \frac{dr}{d\theta} = -\pi \sin(\pi \theta) \) with \( r(0) = 0 \).
Recognize that this is a first-order ordinary differential equation that can be solved by integrating both sides with respect to \( \theta \).
Set up the integral: \( r(\theta) = \int -\pi \sin(\pi \theta) \, d\theta + C \), where \( C \) is the constant of integration.
Perform the integration by using the substitution method or recalling the integral of \( \sin(kx) \), which is \( -\frac{1}{k} \cos(kx) \).
Apply the initial condition \( r(0) = 0 \) to solve for the constant \( C \), then write the final expression for \( r(\theta) \).

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Key Concepts

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

Separable Differential Equations

A separable differential equation can be written as a product of a function of one variable and a function of another, allowing variables to be separated on opposite sides of the equation. This technique simplifies solving by integrating each side independently.
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Initial Value Problems (IVP)

An initial value problem involves solving a differential equation with a given initial condition, which specifies the value of the unknown function at a particular point. This condition helps determine the unique solution among many possible ones.
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Integration of Trigonometric Functions

Solving differential equations involving trigonometric functions requires knowledge of integrating these functions, such as sine and cosine. Recognizing standard integrals and applying them correctly is essential to find the explicit solution.
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