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Monday, April 13, 2015

Separation of Variables, 41

Category: Differential Equations

"Published in Newark, California, USA"

Find the general solution for


Solution:

Consider the given equation above 


Express y' as dy/dx as follows



By separation of variables, transpose dx and (e2x + 4) to the right side of the equation and y to the left side of the equation, we have  



Integrate on both sides of the equation, we have  



Did you notice that the right side of an equation cannot be integrated by simple integration? The differential of e2x + 4 is 2e2xdx and 2e2x is missing at the numerator. Because of this, we have to use the algebraic substitution as follows

Let  

So that 

The value of dx is  


Hence, the above equation becomes





By separating the partial fractions, we can solve for the values of A and B as follows



Equate x0:
                           


Equate x:

                    


Substitute the values of A and B to the above 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