Toronto Math Forum
APM3462015S => APM346Home Assignments => HA1 => Topic started by: Victor Ivrii on January 20, 2015, 06:53:54 AM

Solutions to be posted as a "Reply" only after January 22, 21:00
a. Find the general solution of
\begin{equation}
u_{tt}9u_{xx}=0;
\label{eqHA1.7}
\end{equation}
b. Solve IVP
\begin{equation}
u_{t=0}=\sin(x),\quad u_t_{t=0}=\cos(x)
\label{eqHA1.8}
\end{equation}
for (\ref{eqHA1.7});
c. Consider (\ref{eqHA1.7}) in $\{t>0, \, 3t> x > 3t\}$ and find a solution to it, satisfying Goursat problem
\begin{equation}
u_{x=3t}=t,\quad u_{x=3t}=6t.
\label{eqHA1.9}
\end{equation}
Remark.
Goursat problem for wave equation $u_{tt}c^2u_{xx}=0$ in ${t> 0, ct<x<ct}$ is $u_{x=ct, t>0}=\phi(t)$, $u_{x=ct, t>0}=\psi(t)$ and one often assumes that compatibility condition $\phi(0)=\psi(0)$ is fulfilled. It is very important that $x=\pm ct$ are characteristics.

Attached ;)

By the way Sir, have we talked about the Goursat problem in class? I didn't see it on the notes online. :(

No, we did not talk about Goursat but I defined it in the assignment and you have all tools to handle it (as you demonstrated) :D