Toronto Math Forum
APM3462019 => APM346Lectures & Home Assignments => Home Assignment 1 => Topic started by: Zhiman Tang on January 18, 2019, 07:01:19 PM

u_{xy} = u_{x}u_{y}
I use the hint and divide both sides by u_{x}. I get u_{x} = e^{u} * f(x). I am stuck there. Could anybody help me out?

I would start from the beginning.
$$\frac{u_{xy}}{u_x} = \frac{u_x u_y}{u_x} \Rightarrow \frac{u_{xy}}{u_x} = u_y$$
Integrate both sides,
$$\ln{u_x} = u + f(x)$$
$$u_x = e^{u+f(x)} = e^u \cdot g(x)$$
$$\frac{\partial u}{\partial x} = g(x)e^u$$
$$\frac{\partial u}{e^u} = g(x)\partial x$$
Integrate both sides,
$$e^{u} = G(x) + h(y)$$
$$u(x,y) = \ln (G(x)  h(y))$$
OK. V.I.