Hi! Haven't been on here for ages.

I'm a little confused about part of a question I'm doing. I won't write it all out, but basically u=u(x(s,r), t(s,r))

$\displaystyle \displaystyle \frac{\partial u}{\partial s} = -u$

$\displaystyle \displaystyle \frac{\partial x}{\partial s} = 3x$

$\displaystyle \displaystyle \frac{\partial t}{\partial s} = 1$

From that we supposedly get t = s + A(r) which I do understand, but also:

x=B(r)exp(3s) and u=A(r)exp(-s).

Maybe I'm a bit too tired to be doing this, but where do the exponentials come from?

Thanks!