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http://www.mscs.dal.ca/~iron/math5220/testsol.pdf

I was reviewing this site and for #2, does it look like there is a typo? I am not getting that same discriminant, and a little unclear on the sketch. Can someone please explain it?

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    The discriminant of the PDE $Au_{xx}+2Bu_{xy}+Cu_{yy}=0$ is $B^2-AC$, so I don't think there's any mistake. NB the convention in use here that the coefficient of $u_{xy}$ is written as $2B$.2012-09-10

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