How do I Integrate $2\phi_xs_x + s\phi_{xx} = 0$ to obtain $s^2\phi_x = I$,
where I is a constant.
I have tried working back from $s^2\phi_x = I$, but when I differentiate this I obtain $2\phi_xs_x + s^2\phi_{xx} = 0$.
Just wondering where my error is working backwards, as I cannot see a way to do this.
Many thanks.
Since $(s^2\phi_x)_x=2ss_x\phi_x+s^2\phi_{xx}=s(2\phi_xs_x+s\phi_{xx})=0$, $s^2\phi_x$ is constant.