I'm having problems with finding all possible integers solutions of particular equations, like this one for example: $x^2 -xy + 2y^2 = 29$. What sets me off, is the term $xy$, I don't know how to deal with it.
I know methods for solving equations like $x^2 - 3y^2 = -3$ (then I work with the fundamental unit and with norm forms), but I'm stuck on a method for the first one. Substitutions don't seem to do the trick, but I could be wrong.
As always, any help would be dearly appreciated.