### Author Topic: Spring 2018 Midterm Problem 3 (Both Main and Late)  (Read 324 times)

#### MikeMorris

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##### Spring 2018 Midterm Problem 3 (Both Main and Late)
« 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.