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Ch. 9 - Differential Equations
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Not the one you use?Change textbook
Chapter 9, Problem 9.1.36

33–42. Solving initial value problems Solve the following initial value problems.
y'(x) = 4 sec² 2x, y(0) = 8

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Identify the given differential equation and initial condition: \(y'(x) = 4 \sec^{2}(2x)\) with \(y(0) = 8\).
Recall that to solve the initial value problem, we need to find the antiderivative (integral) of \(y'(x)\) to get \(y(x)\).
Set up the integral: \(y(x) = \int 4 \sec^{2}(2x) \, dx + C\), where \(C\) is the constant of integration.
Use a substitution to integrate: let \(u = 2x\), so \(du = 2 \, dx\) or \(dx = \frac{du}{2}\). Rewrite the integral in terms of \(u\).
Integrate \(4 \sec^{2}(2x) \, dx\) using the substitution, then apply the initial condition \(y(0) = 8\) to solve for \(C\).

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Key Concepts

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

Initial Value Problems (IVPs)

An initial value problem involves a differential equation along with a specified value of the unknown function at a particular point. Solving an IVP means finding a function that satisfies both the differential equation and the initial condition, ensuring a unique solution.
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Initial Value Problems

Integration of Trigonometric Functions

Solving the given differential equation requires integrating the derivative function, which involves trigonometric functions like sec²(2x). Recognizing that the integral of sec²(u) du is tan(u) is essential, along with applying substitution when the argument is a function of x.
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Introduction to Trigonometric Functions

Applying Initial Conditions to Determine Constants

After integrating, the solution includes an arbitrary constant. Using the initial condition y(0) = 8 allows us to substitute x = 0 and y = 8 into the general solution to solve for this constant, yielding the particular solution to the IVP.
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Related Practice
Textbook Question

12–16. Sketching direction fields Use the window [-2, 2] x [-2, 2] to sketch a direction field for the following equations. Then sketch the solution curve that corresponds to the given initial condition. A detailed direction field is not needed.

y(x) = sin y, y(−2) = 1/2

Textbook Question

17–32. Solving initial value problems Determine whether the following equations are separable. If so, solve the initial value problem.

y'(t) = y³sin t, y(0) = 1

Textbook Question

The general solution of a first-order linear differential equation is y(t) = Ce⁻¹⁰ᵗ − 13. What solution satisfies the initial condition y(0) = 4?

Textbook Question

5–10. First-order linear equations Find the general solution of the following equations.


y'(x) = −y + 2

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Textbook Question

21–24. Logistic equations Consider the following logistic equations. In each case, sketch the direction field, draw the solution curve for each initial condition, and find the equilibrium solutions. A detailed direction field is not needed. Assume t ≥ 0 and tP ≥ 0.

P′(t) = 0.05P(1−P/800); P(0) = 100, P(0) = 400, P(0) = 700

Textbook Question

45–48. General first-order linear equations Consider the general first-order linear equation y'(t)+a(t)y(t)=f(t). This equation can be solved, in principle, by defining the integrating factor p(t)=exp(∫a(t)dt). Here is how the integrating factor works. Multiply both sides of the equation by p (which is always positive) and show that the left side becomes an exact derivative. Therefore, the equation becomes


p(t)(y′(t) + a(t)y(t)) = d/dt(p(t)y(t)) = p(t)f(t).


Now integrate both sides of the equation with respect to t to obtain the solution. Use this method to solve the following initial value problems. Begin by computing the required integrating factor.


y′(t) + (2t)/(t² + 1)y(t) = 1 + 3t², y(1) = 4

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