Math Problem Statement

dy/dt= 1/e^-y + e^y y(0)=0

Solution

To solve the differential equation:

dydt=1ey+ey\frac{dy}{dt} = \frac{1}{e^{-y}} + e^y with the initial condition y(0)=0y(0) = 0, let's follow these steps:

Step 1: Simplify the equation

First, notice that:

1ey=ey\frac{1}{e^{-y}} = e^y

Thus, the equation becomes:

dydt=ey+ey=2ey\frac{dy}{dt} = e^y + e^y = 2e^y

Step 2: Separate variables

We can now separate variables by dividing both sides by 2ey2e^y:

12eydy=dt\frac{1}{2e^y} dy = dt

Step 3: Integrate both sides

Now, integrate both sides:

12eydy=dt\int \frac{1}{2e^y} dy = \int dt

The left side is a simple exponential integral, and the right side is just tt. So we get:

12eydy=t\frac{1}{2} \int e^{-y} dy = t

The integral of eye^{-y} is ey-e^{-y}, so:

12ey=t+C-\frac{1}{2} e^{-y} = t + C

Step 4: Solve for yy

Multiply both sides by -2:

ey=2(tC)e^{-y} = 2(-t - C)

Taking the natural logarithm of both sides:

y=ln(2(tC))-y = \ln(2(-t - C))

Thus:

y=ln(2(tC))y = -\ln(2(-t - C))

Step 5: Apply the initial condition y(0)=0y(0) = 0

Substitute t=0t = 0 and y(0)=0y(0) = 0 into the equation:

0=ln(2(0C))0 = -\ln(2(0 - C))

So, ln(2C)=0\ln(-2C) = 0, which means 2C=1-2C = 1 or C=12C = -\frac{1}{2}.

Final solution:

Substitute C=12C = -\frac{1}{2} into the equation:

y=ln(2(t+12))y = -\ln(2(-t + \frac{1}{2}))

This is the solution to the differential equation.

Would you like further details or clarifications?


Here are 5 related questions to expand on this topic:

  1. How would the solution change if the initial condition were different?
  2. What is the behavior of the solution as tt \to \infty?
  3. Can this method be applied to non-exponential differential equations?
  4. How do you check the validity of the solution in this context?
  5. What happens to the solution if the equation includes an additional term?

Tip: Always check your solution by substituting it back into the original differential equation to verify its accuracy.

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Math Problem Analysis

Mathematical Concepts

Differential Equations
Separation of Variables
Exponential Functions

Formulas

dy/dt = 2e^y
∫ e^-y dy = ∫ dt

Theorems

Method of Separation of Variables

Suitable Grade Level

Undergraduate (Calculus I)