Tuesday, 21 April 2015

`(x-1)y' + y = x^2 -1` Solve the first-order differential equation


Given` (x-1)y'+y=x^2-1`


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,


`(x-1)y'+y=x^2-1`


=> `(x-1)[y' + y/(x-1)] = x^2 -1`


=> `y'+y/(x-1)= ((x+1)(x-1))/(x-1)`


=> `y'+y/(x-1)= (x+1)` --------(1)`



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


on comparing both we get,


`p(x) = 1/(x-1) and q(x)=(x+1)`


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)...



Given` (x-1)y'+y=x^2-1`


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,


`(x-1)y'+y=x^2-1`


=> `(x-1)[y' + y/(x-1)] = x^2 -1`


=> `y'+y/(x-1)= ((x+1)(x-1))/(x-1)`


=> `y'+y/(x-1)= (x+1)` --------(1)`



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


on comparing both we get,


`p(x) = 1/(x-1) and q(x)=(x+1)`


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 (1/(x-1))dx) *(x+1)) dx +c)/e^(int(1/(x-1)) dx)`


first we shall solve


`e^(int (1/(x-1)) dx)=e^(ln|x-1|) = |x-1|`  


When `x-1<=0 ` then `ln(x-1)` is undefined , so  


`e^(int(1/(x-1)) dx)=x-1`


so


proceeding further, we get


y(x) =`((int e^(int (1/(x-1))dx) *(x+1)) dx +c)/e^(int(1/(x-1)) dx)`


=`((int (x-1)*(x+1)) dx +c)/(x-1)`


=`((int (x^2-1) ) dx +c)/(x-1)`


= `(x^3/3 -x  +c)/(x-1)`



` y(x)=(x^3/3 -x +c)/(x-1)`


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