/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 30 Find the general solution of eac... [FREE SOLUTION] | 91Ó°ÊÓ

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Find the general solution of each differential equation or state that the differential equation is not separable. If the exercise says "and check," verify that your answer is a solution. $$ y^{\prime}=x-2 x y $$

Short Answer

Expert verified
The general solution is \( y = \frac{1 \mp Ke^{-x^2}}{2} \), where \(K\) is a constant.

Step by step solution

01

Identify the Type of Differential Equation

The given differential equation is \( y' = x - 2xy \). We need to see if it is separable. A separable differential equation can be written in the form \( g(y) dy = f(x) dx \). Let's check if this equation can be transformed into that form.
02

Rearrange the Equation

Rewrite the equation as \( y' = x - 2xy \), which can also be expressed as \( y' = x(1 - 2y) \). This lets us clearly see that we may be able to separate the variables by dividing both sides by \(1 - 2y\).
03

Separate Variables

Divide both sides by \(1 - 2y\) and multiply by \(dx\): \( \frac{dy}{1 - 2y} = x dx \). Now, the variables are separated.
04

Integrate Both Sides

Integrate both sides: \( \int \frac{dy}{1 - 2y} = \int x \, dx \). The left side integrates to \(-\frac{1}{2} \ln |1 - 2y| \) and the right side integrates to \( \frac{x^2}{2} + C \), where \(C\) is the constant of integration.
05

Solve for y

After integrating, we have \(-\frac{1}{2} \ln |1 - 2y| = \frac{x^2}{2} + C \). Multiply through by \(-2\) to isolate \(\ln |1 - 2y| = -x^2 - 2C \). Exponentiate both sides to remove the natural log, yielding \(|1 - 2y| = e^{-x^2 - 2C} \). Let \(e^{-2C} = K\), a new constant, then \(1 - 2y = \pm Ke^{-x^2}\). Thus, solving for \(y\), we get \(y = \frac{1 \mp Ke^{-x^2}}{2}\).
06

Check the Solution

To verify, take the derivative of \(y = \frac{1 - Ke^{-x^2}}{2}\) (we will ignore \(\pm\) here for simplicity) with respect to \(x\) and simplify. This yields \(y' = Kxe^{-x^2}\), which can be substituted back into the original equation \(y' = x - 2xy\) to ensure both sides are equal. If they match, our solution is correct.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Separable Equations
In differential equations, a separable equation is one that can be rewritten to allow the separation of variables. This means you can express the equation such that each variable appears on its own side of the equation with its respective differential. For example, the equation given here is \( y' = x - 2xy \). Our goal is to rewrite it and check if it can be separated.Notice how the equation can be reorganized into \( y' = x(1 - 2y) \). By doing this, we reveal a form that allows separation: \( \frac{dy}{1 - 2y} = x \, dx \). This split means that each variable (\(y\) and \(x\)) appears only with its differential (\(dy\) or \(dx\), respectively).Key steps to identify a separable equation:
  • Rearrange terms to isolate multiplication or division forms.
  • Observe if variables can be separated on opposite sides of the equation.
  • Check if both sides have a consistent and meaningful differential (\(dy\) and \(dx\)).
Integration Techniques
Once you have successfully separated a differential equation, it’s time to integrate both sides. Integration allows you to solve for the function that the differential equation describes.In this scenario, the separated equation \( \frac{dy}{1 - 2y} = x \, dx \) requires us to integrate each side:- The left side becomes \( \int \frac{dy}{1 - 2y} \).- The right side becomes \( \int x \, dx \).The integration process:
  • For the left side, you recognize the form of the integral as \(-\frac{1}{2} \ln |1 - 2y| \).
  • For the right side, the integral is straightforward, \( \frac{x^2}{2} + C \), with \( C \) as the integration constant.
These results offer expressions for each integral that come together to give a more complete picture of the solution.
General Solution
The general solution is a key outcome when solving differential equations, representing a family of solutions rather than a single one. After integrating the separated equation, you reach an expression like \(-\frac{1}{2} \ln |1 - 2y| = \frac{x^2}{2} + C \).The steps to find the general solution are:
  • Eliminate the logarithm by exponents to solve for the function \(y\).
  • Result in the simplified form \(|1 - 2y| = e^{-x^2 - 2C}\). Substitute \(e^{-2C}\) by a constant \(K\), yielding \(1 - 2y = \pm Ke^{-x^2}\).
  • Finally, isolate \(y\) so that \(y = \frac{1 \mp Ke^{-x^2}}{2}\).
This general solution contains arbitrary constants indicating an infinite number of possible specific solutions, depending on initial conditions. Solver can check if the obtained expression satisfies the original equation and aligns with any given initial conditions in a more specific problem scenario.

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Most popular questions from this chapter

Solve each differential equation and initial condition and verify that your answer satisfies both the differential equation and the initial condition. $$\left\\{\begin{array}{l} y^{\prime}=y^{2} e^{x}+y^{2} \\ y(0)=1 \end{array}\right.$$

An algae bloom in a lake is a sudden growth of algae that consumes nutrients and blocks sunlight, killing other life in the water. Suppose that the number of tons \(y(t)\) of algae after \(t\) weeks satisfies $$ \begin{array}{l} y^{\prime}=t y+t \\ y(0)=2 \end{array} $$ a. Solve this differential equation and initial condition. b. Use your solution to find the amount of algae after 2 weeks. c. Graph the solution on a graphing calculator and find when the algae bloom will reach 40 tons.

The total number \(y(t)\) of cases of AIDS (acquired immunodeficiency syndrome) diagnosed in a certain region after \(t\) years satisfies $$ \begin{array}{l} y^{\prime}-\frac{3}{t} y=0 \\ y(1)=125 \end{array} $$ a. Solve this differential equation and initial condition. (Your solution will show that AIDS does not spread logistically, as do most epidemics, but like a power. This means that AIDS will spread more slowly, which seems to result from its being transmitted at different rates within different subpopulations. b. Use your solution to predict the number of AIDS cases in the region by the year \(t=15\)

Think of the slope field for the differential equation \(\frac{d y}{d x}=x y .\) What is the sign of the slope in quadrant \(I\) (where \(x\) and \(y\) are both positive)? What is the sign of the slope in each of the other three quadrants? Check your answers by looking at the slope field on page 596.

For each initial value problem: a. Use an Euler's method graphing calculator program to find the estimate for \(y(2)\). Use the interval [0,2] with \(n=50\) segments. b. Solve the differential equation and initial condition exactly by separating variables or using an integrating factor. c. Evaluate the solution that you found in part (b) at \(x=2\). Compare this actual value of \(y(2)\) with the estimate of \(y(2)\) that you found in part (a). $$ \begin{array}{l} \frac{d y}{d x}=-y \\ y(0)=1 \end{array} $$

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