I need to solve:
Ln(y^x). dy/dx = 3x^2 . y
Rearrange to get
X.lny (dy) = 3x^2 (dx)
Int (X.lny (dy)) = Int (3x^2 (dx))
(lny)^2/2 = 3x^2/2 + C
According to my mark scheme I should get C/2
But I don't know why?
First order differential equation Watch
- Thread Starter
- 19-04-2012 17:28
- 19-04-2012 17:36
- try integrating by parts (where u = ln y, and dv/dy = 1)And if you're finding c, then you'll have been given x and y values which you haven't stated in your post.
Also, I don't see where your y from the first line has gone.
Edit: And ignore the first two parts as they have been corrected below - next time try and keep the y in your working throughout, but equally (if not more so) it's my bad for not trying with it first ).Last edited by starkrush; 19-04-2012 at 17:57.
- 19-04-2012 17:39
let u= lny
du/dy = 1/y
-> I u du = u^2/2= (lny)^2/2.
- 19-04-2012 17:42
Wolfram says no constant/2.
Not quite sure where that constant/2 has come from, I certainly don't get that either.
- 19-04-2012 17:44
OP is correct, if I'm interpreting correctly.Last edited by f1mad; 19-04-2012 at 17:46.
- 19-04-2012 17:56
And edited to reflect this clearerLast edited by starkrush; 19-04-2012 at 17:58.
(Original post by starkrush)
- 19-04-2012 18:00
Ninja edited 1 minute before you replied
And edited to reflect this clearer
Last edited by starkrush; 1 Minute Ago at 16:57.
- 19-04-2012 18:12
That was to strikethrough the text!
(Yes, this is very constructive maths help)