# Changes

$\frac{\partial M}{\partial y} = \frac{\partial N}{\partial t}$
To find the solution of this equation, we assume that the solution is &phi; = constant. We can re-write a different form of this equation by substituting $\frac{\partial \phi}{\partial t} = M$ and $\frac{\partial \phi}{\partial y} = N$. This yields $(\frac{\partial \phi}{\partial t}) dt + (\frac{\partial \phi}{\partial y}) dy = 0$, which makes sense.