MHB Solve Cauchy Problem: Help Needed with Separate Variable Method

[Julio1]

Solve the Cauchy problem:

\begin{align}
\dfrac{dx}{dr} &= y\\
x(0,s) &= s
\end{align}

Help please, I don't remember how solve this :(. Separate variable isn't the method?

 

[evinda]

Solve the Cauchy problem:

\begin{align}
\dfrac{dx}{dr} &= y\\
x(0,s) &= s
\end{align}

Help please, I don't remember how solve this :(. Separate variable isn't the method?

Is it surely $\frac{dx}{dr}$ ?