# Toronto Math Forum

## APM346--2019 => APM346--Misc => Topic started by: MikeMorris on February 25, 2019, 07:24:53 PM

Title: Spring 2018 Midterm Problem 3 (Both Main and Late)
Post by: MikeMorris on February 25, 2019, 07:24:53 PM
The solutions given to these questions make absolutely no sense to me. If the PDE is $u_{tt} - u_{xx} = 0$, how could the general solution possible be $u(x,t) = \phi(x+3t) + \psi(x-3t)$?  We have $c^{2} = 1$, so shouldn't it be $\phi(x+t) + \psi(x-t)$? I am completely lost.
Title: Re: Spring 2018 Midterm Problem 3 (Both Main and Late)
Post by: Victor Ivrii on February 26, 2019, 04:15:46 PM
Misprints. Corrected