Supposedly simple differential equation

In summary, the problem involves finding the solution to the differential equation dy/dt = 1/(e^y - t) with initial condition y(1) = 0. The equation is not separable, so the suggestion is to try a substitution u = e^y - t. This leads to a separable equation which can be solved using basic integration techniques. Another approach is to switch the variables and find t(y), which results in a simpler ODE that can be easily integrated.
  • #1
popo902
60
0

Homework Statement


Find the solution of
dy/dt = 1/ (e^y -t), y(1) = 0


Homework Equations





The Attempt at a Solution


i tried separating the equation, but the subtraction gets in the way
well this is what i have
y = t - 1 + C/e^t
i solved for t then i put that into the single order ODE formula
but the answer is y = arccosht
...so...
can someone give me a hint on how to start this?
 
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  • #2
Yes, the fact that an equation is not separable does make it hard to separate!

Here's what I would try. Since it is the [itex]e^y- t[/itex] that is the problem, let [itex]u= e^y- t[/itex] so that
[tex]\frac{dy}{dt}= \frac{1}{u}[/tex]
and since [itex]e^y= u+ t[/itex]
[tex]e^y\frac{dy}{dt}= \frac{du}{dt}+ 1[/tex]
[tex](u+ t)\frac{1}{u}= \frac{du}{dt}+ 1[/tex]
[tex]\frac{du}{dt}= \frac{u+t}{u}- 1= \frac{t}{u}[/tex]
which is separable.
 
  • #3
Well, you can switch the variables and try to find t(y). The ODE which results

[tex] \frac{dt(y)}{dy} + t(y) = e^y [/tex]

should be very easy to integrate, right ?
 
  • #4
Well, if you want to do it the easy way! :tongue2:
 

1. What is a differential equation?

A differential equation is a mathematical equation that relates the rate of change of a quantity to the quantity itself. It involves one or more variables, their derivatives, and the function itself. Differential equations are used to model a wide range of phenomena in physics, engineering, and other scientific fields.

2. How do you solve a differential equation?

The method of solving a differential equation depends on its type and complexity. Some common techniques include separation of variables, substitution, and using integral calculus. In some cases, a differential equation can only be solved numerically using computer software.

3. What is the difference between ordinary and partial differential equations?

Ordinary differential equations involve one independent variable, while partial differential equations involve multiple independent variables. Ordinary differential equations can be solved using techniques such as separation of variables, while partial differential equations require more advanced methods such as Fourier transforms or numerical methods.

4. Can differential equations be used in real-world applications?

Yes, differential equations are used extensively in real-world applications to model and understand complex systems and phenomena. For example, they are used in physics to describe the motion of objects, in biology to model population growth, and in economics to study economic systems.

5. Are there different types of differential equations?

Yes, there are many different types of differential equations, including linear and nonlinear, first-order and higher-order, and ordinary and partial. Each type has its own unique properties and methods for solving. Additionally, there are also specific types of differential equations used for specific applications, such as the heat equation in thermodynamics or the Schrödinger equation in quantum mechanics.

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