# Thread: Quiestion to do with existence and uniqueness of a equation

1. ## Quiestion to do with existence and uniqueness of a equation

Hi

My question is
Consider the initial value problem

$yy'=x-1$

subject to the intitial condition $y(x=X)=Y$ where X and Y are constants.

a)For which values of X and Y does the existence and uniqueness theorem ensure the existence of a unique solution? If a unique solution can be shown to exist, will it exist for all values of $x$.

b)Find the general solution of the ODE, using any suitable method.

In my notes i have a section on uniqueness of solutions but its not very detailed. It mentions Peano existence theorem and also mentions picard existence theorem.

I wanted to know what the difference what between these two theorems also.

thanks

2. If we write the DE in 'standard form'...

$y^{'}= f(x,y)$ , $y(x_{0})=y_{0}$ (1)

... the solution exists and is unique if $f(*,*)$ is 'Lipschitz continous' in $(x_{0}, y_{0})$ and clearly that is not verified for $y_{0}=0$...

The DE can be written in the form...

$y\cdot dy = (x-1)\cdot dx$ (2)

... so that the variables are 'separated' and the DE can be solved with simple integration...

Kind regards

$\chi$ $\sigma$