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Monday, July 21, 2014

Solving Equations - Homogeneous Functions, 11

Category: Differential Equations

"Published in Newark, California, USA"

Find the general solution for


Solution:

Consider the given equation above 


Did you notice that the given equation cannot be solved by separation of variables? The trigonometric function is a combination of x and y in the group and there's no way that we can separate x and y.  

This type of differential equation is a homogeneous function. Let's consider this procedure in solving the given equation as follows   
 



Let


so that


Substitute the values of y and dy to the given equation, we have






The resulting equation can now be separated by separation of variables as follows   




Integrate on both sides of the equation, we have 






Take the inverse natural logarithm on both sides of the equation, we have





But



Hence, the above equation becomes 



Therefore, the general solution is

 

Sunday, July 20, 2014

Separation of Variables, 18

Category: Differential Equations

"Published in Newark, California, USA"

Find the general solution for


Solution:

Consider the given equation above 


Transfer all the terms from the right side of the equation to the left side of the equation and group as follows


 

In order to separate dx and dy from other variables, divide both sides of the equation by (1 - y²)(1 + x²) as follows
 
 


Integrate both sides of the equation, we have




Next, we need to solve for the value of A and B by partial fractions as follows



Equate the coefficients for y, we have



Equate the coefficients for y0, we have 





Substitute the value of A and B to the above equation, we have









Take the inverse natural logarithm on both sides of the equation, we have


  
 
 



where D = C².

Therefore, the general solution is

Saturday, July 19, 2014

Separation of Variables, 17

Category: Differential Equations

"Published in Newark, California, USA"

Find the general solution for


Solution:

Consider the given equation above 


In order to separate dx and dy from other variables, divide both sides of the equation by cos² x cos² y as follows


 



Integrate both sides of the equation, we have 


 

Therefore, the general solution is