Sunday 30 March 2014

`y' = x(1+y)` Solve the differential equation

 An ordinary differential equation (ODE) has differential equation for a function with single variable. A first order ODE follows `(dy)/(dx)= f(x,y)` .


It can also be in a form of `N(y) dy= M(x) dx` as variable separable differential equation.


 To be able to set-up the problem as `N(y) dy= M(x) dx` , we let `y' = (dy)/(dx)` .


 The problem: `y'=x(1+y)` becomes:


`(dy)/(dx)=x(1+y)`


Rearrange by cross-multiplication, we get:


`(dy)/(1+y)=xdx`


Apply direct integrationon both sides:...

 An ordinary differential equation (ODE) has differential equation for a function with single variable. A first order ODE follows `(dy)/(dx)= f(x,y)` .


It can also be in a form of `N(y) dy= M(x) dx` as variable separable differential equation.


 To be able to set-up the problem as `N(y) dy= M(x) dx` , we let `y' = (dy)/(dx)` .


 The problem: `y'=x(1+y)` becomes:


`(dy)/(dx)=x(1+y)`


Rearrange by cross-multiplication, we get:


`(dy)/(1+y)=xdx`


Apply direct integration on both sides: `int (dy)/(1+y)= int xdx` to solve for the general solution of a differential equation.


For the left side, we consider u-substitution by letting:


`u= 1+y` then `du = dy`


The integral becomes:  `int(dy)/(1+y)=int(du)/(u)`


 Applying basic integration formula for logarithm:


`int(du)/(u)=ln|u|`


Plug-in `u = 1+y` on `ln|u|` , we get:


`int(dy)/(1+y)=ln|1+y|`


For the right side, we apply the Power Rule of integration: `int x^n dx = x^(n+1)/(n+1)+C`


`int x* dx= x^(1+1)/(1+1)+C`


             ` = x^2/2+C`


Combining the results from both sides, we get the general solution of the differential equation as:


`ln|1+y|= x^2/2+C`


or


`y =e^((x^2/2+C))-1`

No comments:

Post a Comment

In "By the Waters of Babylon," under the leadership of John, what do you think the Hill People will do with their society?

The best place to look for evidence in regards to what John's plans are for his people is the final paragraphs of the story. John has re...