Monday, September 15, 2014

`dy/dx + 2y/x = 3x-5` Solve the first-order differential equation

Given` dy/dx+2y/x=3x-5`


`y'+2y/x=3x-5`


when the first order linear ordinary Differentian equation has the form of


`y'+p(x)y=q(x)`


then the general solution is ,


`y(x)=((int e^(int p(x) dx) *q(x)) dx +c)/e^(int p(x) dx) `


so,


`y'+2y/x=3x-5--------(1)`


`y'+p(x)y=q(x)---------(2)`


on comparing both we get,


`p(x) = 2/x and q(x)=3x-5`


so on solving with the above general solution we get:


y(x)=`((int e^(int p(x) dx) *q(x)) dx +c)/e^(int p(x) dx) `


=`((int e^(int 2/x dx) *(3x-5)) dx +c)/e^(int 2/x dx)`


first we shall solve


`e^(int 2/x dx)=e^(2ln(x)) =x^2`     


so


proceeding further, we get


y(x) =`((int e^(int 2/x dx) *(3x-5)) dx +c)/e^(int 2/x dx)`


=`((int x^2 *(3x-5)) dx +c)/x^2`


=`((int (3x^3 -5x^2) ) dx +c)/x^2`


= `(3x^4 /4 -5x^3/3+c)/x^2 `


so `y(x)=(3x^4 /4 -5x^3/3+c)/(x^2 )`

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