ed84c Posted May 22, 2008 Share Posted May 22, 2008 I'm struggling to understand what is a proof in modular arithmetic and what does not. Example below; a = b(mod M) c=d(mod M) 1) Prove: a + c = b + d (mod M); a = b + hM c = d + kM hence; a + c = b + d (h +k)M a + c = b + d (mod M). No problem so far. Now; 1) ac = bd (mod M) ac = (b + hM)(d + kM) ac = bd + bkM + dhM + hkM^2 To me- that isnt ac = bd (mod M) -> what am I missing? Secondly; a - c = b - d + (h-k)M which to me IS a correct modular arithemtic calculation i.e. a-c=b-d (mod M). Aparantly it's not thought? Link to comment Share on other sites More sharing options...

D H Posted May 22, 2008 Share Posted May 22, 2008 ac = bd + bkM + dhM + hkM^2 To me- that isnt ac = bd (mod M) -> what am I missing? What is (bkM + dhM + hkM^2) mod M? Link to comment Share on other sites More sharing options...

ed84c Posted May 22, 2008 Author Share Posted May 22, 2008 0......... So that makes ac = bd mod(M), then, right? Link to comment Share on other sites More sharing options...

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