Thursday, 13 March 2014

number theory - Find integer solutions to linear congruence




Find all integer solutions of 2n12mod19



So I have re-arranged to: 2x19y=12 and by the extended Euclidean Algorithm, I get x=1 
y=9



However, this is how far I was able to get to and not sure what follow past this point? What exactly are we looking for?


Answer



I would say there are infinitely many. Another way to think of 2n \equiv 12 \pmod{19} is that 2n - 12 = 19k for some k \in \mathbb{Z}. So n = \frac{19k + 12}{2}. Thus any even k will produce an integer solution.



EDIT: It might be better to think in terms of equivalence classes for the sake of negative k values. So maybe [n] = \bigl[\frac{19k + 12}{2}\bigr] in \mathbb{Z}_{19}. For example: If k = -2, then [n]_{19} = [-13]_{19} = [6]_{19}.



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