Math Problem Statement

y' = (2y-1) sinx cosx

Solution

The given differential equation is:

y=(2y1)sin(x)cos(x)y' = (2y - 1) \sin(x) \cos(x)

This is a first-order linear differential equation where the right-hand side involves both yy and xx. To solve this equation, we can attempt separation of variables. Let's go through the steps:

Step 1: Simplify the right-hand side

Recall the trigonometric identity: sin(2x)=2sin(x)cos(x)\sin(2x) = 2 \sin(x) \cos(x) Thus, we can rewrite the equation as: y=(2y1)12sin(2x)y' = (2y - 1) \frac{1}{2} \sin(2x) or y=12(2y1)sin(2x)y' = \frac{1}{2} (2y - 1) \sin(2x)

Step 2: Separation of variables

We want to isolate the terms involving yy on one side and those involving xx on the other side.

dydx=12(2y1)sin(2x)\frac{dy}{dx} = \frac{1}{2} (2y - 1) \sin(2x)

Now, divide both sides by 2y12y - 1 and multiply both sides by dxdx:

dy2y1=12sin(2x)dx\frac{dy}{2y - 1} = \frac{1}{2} \sin(2x) dx

Step 3: Integrate both sides

Next, we integrate both sides:

  1. For the left-hand side: The integral of 12y1\frac{1}{2y - 1} is: dy2y1=12ln2y1\int \frac{dy}{2y - 1} = \frac{1}{2} \ln |2y - 1|

  2. For the right-hand side: The integral of 12sin(2x)\frac{1}{2} \sin(2x) is: 12sin(2x)dx=14cos(2x)\int \frac{1}{2} \sin(2x) \, dx = -\frac{1}{4} \cos(2x)

So, after integrating both sides, we get:

12ln2y1=14cos(2x)+C\frac{1}{2} \ln |2y - 1| = -\frac{1}{4} \cos(2x) + C

Step 4: Solve for yy

Multiply both sides of the equation by 2:

ln2y1=12cos(2x)+2C\ln |2y - 1| = -\frac{1}{2} \cos(2x) + 2C

Now, exponentiate both sides to remove the logarithm:

2y1=e12cos(2x)+2C=e2Ce12cos(2x)|2y - 1| = e^{-\frac{1}{2} \cos(2x) + 2C} = e^{2C} e^{-\frac{1}{2} \cos(2x)}

Let e2C=Ae^{2C} = A (where AA is a constant), so the equation becomes:

2y1=Ae12cos(2x)|2y - 1| = A e^{-\frac{1}{2} \cos(2x)}

Finally, remove the absolute value by introducing a constant BB (which can be positive or negative):

2y1=Be12cos(2x)2y - 1 = B e^{-\frac{1}{2} \cos(2x)}

Solve for yy:

y=12+B2e12cos(2x)y = \frac{1}{2} + \frac{B}{2} e^{-\frac{1}{2} \cos(2x)}

Final Solution

The general solution to the differential equation is:

y=12+B2e12cos(2x)y = \frac{1}{2} + \frac{B}{2} e^{-\frac{1}{2} \cos(2x)}

Where BB is an arbitrary constant.


Would you like more details on any part of the solution, or do you have any questions about this process?

Here are 5 related questions to help deepen your understanding:

  1. How can you determine the value of the constant BB if an initial condition is provided?
  2. What are other methods for solving first-order differential equations?
  3. What happens if you have a non-linear differential equation like y=y2sin(x)y' = y^2 \sin(x)?
  4. How can you check if the solution y=12+B2e12cos(2x)y = \frac{1}{2} + \frac{B}{2} e^{-\frac{1}{2} \cos(2x)} is correct by substitution?
  5. How do solutions to differential equations relate to the behavior of physical systems like population models or radioactive decay?

Tip: Always simplify the right-hand side of the differential equation as much as possible before attempting separation of variables. It can make integration easier!

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Math Problem Analysis

Mathematical Concepts

First-Order Differential Equations
Separation of Variables
Trigonometric Identities
Integration

Formulas

sin(2x) = 2sin(x)cos(x)
∫(dy / (2y - 1)) = (1/2) ln|2y - 1|
∫sin(2x) dx = -1/4 cos(2x)

Theorems

Separation of Variables
Logarithmic Integration
Exponential Solutions to Differential Equations

Suitable Grade Level

College-Level