Differential Equation, Bernoulli

In summary, the conversation discusses the use of Bernoulli's equation to solve an equation involving y and e^-x. The correct substitution v=e^(-x)*(x+c) is given, but the person is confused about how to apply it in Bernoulli's formula. After some discussion, they realize their mistake and are able to solve the equation correctly.
  • #1
H2instinct
20
0

Homework Statement



3y^2*y'+y^3= e^-x



The Attempt at a Solution



I am using Bernoulli's equation to substitute V in and I keep coming out with
Y^3= e^x(-e^-x+c)

my V = y^3
Y = v^(1/3)
and dy/dv=(1/3)v^(-2/3)

I peeked to see if I was correct, the right answer is supposed to be Y^3 = e^-x (x+c)

Where did I go wrong?
 
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  • #2
v=y^3 is certainly a good substitution to use, and v=e^(-x)*(x+c) is certainly the correct answer. What I don't understand is how you used Bernoulli's equation to get a wrong answer. Can you explain?
 
  • #3
Dick said:
v=y^3 is certainly a good substitution to use, and e^(-x)*(x+c) is certainly the correct answer. What I don't understand is how you used Bernoulli's equation to get a wrong answer. Can you explain?

Ok I will try and explain what I did:

After getting those substitutions I applied them all to the original equation and got out:

(1/3)v(-2/3)* Dv/Dx + (1/3)v(1/3) = (1/(3ex))*v(-2/3)

Multiplied by the inverse of dy/dv to get:

dv/dx + v = 1/(ex)

This is where I got confused, the function I am supposed to put into Bernoulli's formula usually lies in front of V, so I figured I would use 1, so I did:

eintegral(1, dx) = ex

Multiplied both sides by this and integrated to get the answer that I got. I hope I better explained what I did. Do you see where I went wrong, because I still do not.

EDIT: When I multiplied both sides by ex I seemed to have spaced and not multiplied the RHS... Thus giving me 1 on the right hand side which integrates to be x+C, thus giving me the correct answer... Having me go back through it really helped me figure out what I did wrong. Thanks for helping.
 
Last edited:
  • #4
P.S. I really love this forum, everyone is so helpful!
 
  • #5
Ok, so now you've got e^x*v'+e^x*v=1, right? That's (e^x*v)'=1. Integrate both sides then solve for v.
 

Related to Differential Equation, Bernoulli

1. What is a differential equation?

A differential equation is a mathematical equation that relates a function with one or more of its derivatives. It is used to model and describe the relationship between changing quantities in various scientific fields, such as physics, engineering, and economics.

2. Who is Bernoulli and what is his contribution to differential equations?

Daniel Bernoulli was a Swiss mathematician who made significant contributions to the development of differential equations. He introduced the concept of "Bernoulli's equation," which is a type of differential equation used to model the flow of fluids. He also developed the Bernoulli principle, which explains the relationship between pressure and speed in a moving fluid.

3. What is the difference between an ordinary differential equation and a partial differential equation?

An ordinary differential equation involves only one independent variable, while a partial differential equation involves multiple independent variables. Ordinary differential equations are used to describe systems that change over time, while partial differential equations are used to describe systems that change over both time and space.

4. How is a Bernoulli differential equation solved?

A Bernoulli differential equation is solved by using a substitution technique. This involves substituting the original dependent variable with a new variable, which transforms the equation into a linear differential equation. Then, the linear equation can be solved using standard techniques, and the solution is then substituted back to find the solution to the original Bernoulli equation.

5. What are some real-life applications of Bernoulli differential equations?

Bernoulli differential equations have many real-life applications, such as predicting the airflow around an airplane wing, determining the optimal shape of a sail for a boat, and modeling the spread of infectious diseases. They are also used in economics to model supply and demand, in finance to model stock prices, and in chemistry to model chemical reactions.

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