How to solve that eqation?
Express one variable in terms of the other (see which makes most sense). What are the conditions for having integer solutions?
That is the same as saying that [itex]3^x= 1[/itex] (mod 4). Check out "Fermat's Little Theorem".
Ok, but how can I show that this eqation can be saying like that you wrote? If I place for 3^x=1(mod 4) to top equation and from Fermat's little theorem I have x=3 than I have equation with one variable? That you thought about?
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