Separable differential equation

Dusty912
Messages
149
Reaction score
1

Homework Statement


Solve each of the following differential equations:
4xydx + (x2 +1)dy=0

Homework Equations


None

The Attempt at a Solution


4xydx + (x2 +1)dy=0
(x2 +1)dy=-4xydx
dy/y=-(4xdx)/(x2 +1)
∫dy/y=∫-(4xdx)/(x2 +1)
ln|y|=-2ln|x2+1| +C

used u-sub on last step fo u=x2 +1
 
Physics news on Phys.org
Dusty912 said:

Homework Statement


Solve each of the following differential equations:
4xydx + (x2 +1)dy=0

Homework Equations


None

The Attempt at a Solution


4xydx + (x2 +1)dy=0
(x2 +1)dy=-4xydx
dy/y=-(4xdx)/(x2 +1)
∫dy/y=∫-(4xdx)/(x2 +1)
ln|y|=-2ln|x2+1| +C

used u-sub on last step fo u=x2 +1
Do you have a question?
Your work looks fine to me, but you need to take it one step further and solve for y as a function of x.

After that, check your solution by verifying that it satisifies the original DE.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
Back
Top