Sunday, 24 November 2013

`3(y-4x^2)dx + xdy = 0` Solve the first-order differential equation by any appropriate method

Given` 3(y-4x^2)dx + xdy = 0`


=>` 3y - 12x^2 +xdy/dx=0`


=>` ( 3y - 12x^2)/x +dy/dx=0`


=>` 3y/x - 12x +dy/dx=0`


=> `y'+(3/x)y=12x`


when the first order linear ordinary differential 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'+(3/x)y=12x--------(1)`


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


on comparing both we get,


`p(x) = (3/x) and q(x)=12x`


so on solving with the above general...

Given` 3(y-4x^2)dx + xdy = 0`


=>` 3y - 12x^2 +xdy/dx=0`


=>` ( 3y - 12x^2)/x +dy/dx=0`


=>` 3y/x - 12x +dy/dx=0`


=> `y'+(3/x)y=12x`


when the first order linear ordinary differential 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'+(3/x)y=12x--------(1)`


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


on comparing both we get,


`p(x) = (3/x) and q(x)=12x`


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 (3/x) dx) *((12x)) dx +c)/e^(int (3/x) dx)`


first we shall solve


`e^(int (3/x) dx)=e^(ln(x^3))=x^3`     


so proceeding further, we get


y(x) =`(int e^(int (3/x) dx) *((12x)) dx +c)/e^(int (3/x) dx)`


=`(int x^3 *((12x)) dx +c)/x^3`


=`(int 12x^4 dx +c)/x^3`


 `=(12x^5/5 +c ) /x^3`


so `y=(12x^5/5 +c )/x^3`

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