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Stuck in solving a (rather simple) differential equation problem.

  • Thread starter jowjowman
  • Start date
  • #1
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Homework Statement


Equation: dy/dx=x+1/3y^2 where y>0


Homework Equations


I'm to show that (1/2x^2+x+8)^1/3 is a solution


The Attempt at a Solution


Splitting it up in x/3y^2+1/3y^2 has been futile and I'm out of ideas.

Can anyone help me see the light?

Homework Statement





Homework Equations





The Attempt at a Solution

 

Answers and Replies

  • #2
HallsofIvy
Science Advisor
Homework Helper
41,794
925

Homework Statement


Equation: dy/dx=x+1/3y^2 where y>0
Is this 1+ (1/3)y^2 or 1+ 1/(3y^2) or (x+ 1)/(3y^2)?


Homework Equations


I'm to show that (1/2x^2+x+8)^1/3 is a solution
So you are NOT required to solve the equation? If y= ((1/2)x^2+ x+ 8)^(1/3), what is y'? Of course, y^2= ((1/2)x^3+ x+ 8)^(2/3). Put those into the equation and show that the the equation is satisfied.


The Attempt at a Solution


Splitting it up in x/3y^2+1/3y^2 has been futile and I'm out of ideas.

Can anyone help me see the light?

Homework Statement





Homework Equations





The Attempt at a Solution

 
  • #3
epenguin
Homework Helper
Gold Member
3,632
702
Yes, like many other problems in math, it is easier to solve a differential equation when you know the solution.

That may seem like cheating, but actually a rather well kept secret is that the only way to solve a differential equation is to know the solution, at least in outline.

Perhaps this concept can be further generalised. :shy:
 
  • #4
9
0
Thanks HallsofIvy, you saved my day.
 

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