How Do You Calculate This Indefinite Integral in a First Order Linear ODE?

In summary, a first order linear ODE is a mathematical equation that relates a function and its derivatives, where the function and its derivatives are only raised to the first power and there are no products or powers of the function or its derivatives. The most common method for solving it is using an integrating factor, and an initial value problem involves finding a particular solution that satisfies a given condition at a specific point. The main difference between a first order linear ODE and a first order non-linear ODE is the form of the equation, and first order linear ODEs are used in various real-world applications to model physical phenomena and relationships between variables.
  • #1
Naincy
6
0
Hi

How do you calculate the following indefinite integral:

\(\displaystyle \int \frac{2x}{125+3t} dt\)

a step by step solution would be appreciated
 
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  • #2
Hello and welcome to MHB! :D

I have moved your post to its own thread in our Calculus forum so it will get more prompt attention. New questions should be posted in a new thread in the most appropriate sub-forum.

Now, is it possible you mean:

\(\displaystyle \int\frac{2t}{125+3t}\,dt\)

If so, can you tell us what you have tried so we know where you are stuck?
 
  • #3
Hi. Thanx

No, it is actually 2x and not 2t in the numerator.
It is a function in two variables x and t. I need to integrate it with respect to t. Note that x cannot be considered a constant here.
so , it becomes integration of a function in two variables. i don't know how to start with it.
any help would be appreciated.

- - - Updated - - -

Naincy said:
Hi. Thanx

No, it is actually 2x and not 2t in the numerator.
It is a function in two variables x and t. I need to integrate it with respect to t. Note that x cannot be considered a constant here.
so , it becomes integration of a function in two variables. i don't know how to start with it.
any help would be appreciated.

Basically, I need to find the solution in x for the following differential equation:
dx/dt = 1 - { 2x/(125 + 3t) }
 
  • #4
Naincy said:
Basically, I need to find the solution in x for the following differential equation:
dx/dt = 1 - { 2x/(125 + 3t) }

Oh, okay, that's a different problem entirely, and I can actually help you here. Let's first write the ODE in standard linear form:

\(\displaystyle \frac{dx}{dt}+\frac{2}{3t+125}x=1\)

Now, we need to compute the integrating factor \(\displaystyle \mu(t)=\exp\left(\int\frac{2}{3t+125}\,dt\right)\)

What do you find?

I am going to move and re-title this thread. :D
 
  • #5
MarkFL said:
Now, we need to compute the integrating factor \(\displaystyle \mu(t)=\exp\left(\int\frac{2}{3t+125}\,dt\right)\)

What do you find?

I am going to move and re-title this thread. :D

okay! right. So , i solved this linear first order differential equation and i got

x(t) =

\(\displaystyle \frac{125+3t}{2}\left[1+c({125+3t})^{-5/3}\right]\)

Can you just check if it's correct? Thanx. :)
 
  • #6
Integrating factor,here, is: (125+3t)^(2/3)
 
  • #7
It's close, but not quite correct. If you show your work, we can figure out where the small error is. :D
 
  • #8
Did I get the integrating factor right ?
 
  • #9
Naincy said:
Did I get the integrating factor right ?

Yes.
 
  • #10
ok. figured out the mistake. :)

The final answer is:

x(t) = \(\displaystyle \frac{125+3t}{5} + \frac{c}{({125+3t})^{2/3}}\)

I think this is correct. yeah ?
 
  • #11
Naincy said:
ok. figured out the mistake. :)

The final answer is:

x(t) = \(\displaystyle \frac{125+3t}{5} + \frac{c}{({125+3t})^{2/3}}\)

I think this is correct. yeah ?

Yeah. ;)
 
  • #12
Yes, that's correct. (Yes)
 

FAQ: How Do You Calculate This Indefinite Integral in a First Order Linear ODE?

What is a first order linear ODE?

A first order linear ODE (ordinary differential equation) is a mathematical equation that relates a function and its derivatives. It is called "linear" because the function and its derivatives are only raised to the first power and there are no products or powers of the function or its derivatives. The general form of a first order linear ODE is dy/dx + P(x)y = Q(x), where P(x) and Q(x) are functions of x.

How do you solve a first order linear ODE?

The most common method for solving a first order linear ODE is by using an integrating factor. This involves multiplying both sides of the equation by an integrating factor, which is a function of x that makes the left side of the equation equal to the derivative of the product of the integrating factor and the function y. After multiplying and simplifying, the equation can be integrated to solve for y.

What is an initial value problem in a first order linear ODE?

An initial value problem is a type of differential equation that has an initial condition, usually written as y(x0) = y0, where x0 is a given value and y0 is the value of the function at that point. In other words, an initial value problem involves finding a particular solution to a differential equation that satisfies a given condition at a specific point.

What is the difference between a first order linear ODE and a first order non-linear ODE?

The main difference between a first order linear ODE and a first order non-linear ODE is the form of the equation. A linear ODE has the form dy/dx + P(x)y = Q(x), while a non-linear ODE has a more complex form, such as dy/dx = P(x)y + Q(x). Non-linear ODEs are generally more difficult to solve and may require numerical methods.

How are first order linear ODEs used in real-world applications?

First order linear ODEs are used to model a wide range of physical phenomena, such as population growth, chemical reactions, and electrical circuits. They are also used in engineering and economics to describe relationships between variables. Solving first order linear ODEs allows us to make predictions and understand the behavior of these systems.

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