Testwiki:Reference desk/Archives/Mathematics/2008 July 19

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July 19

Mod Inverse Formula

What is the mod inverse formula is in simple terms?--Melab-1 (talk) 18:03, 19 July 2008 (UTC)

I don't know any formula by that name, and google has nothing. Can you try to explain what formula you're talking about? Algebraist 18:20, 19 July 2008 (UTC)

Are you talking about:

$57\equiv 7mod50$

$x57\equiv 1mod50$

where x is the inverse of 57 (mod 50)

122.107.219.245 (talk) 00:13, 20 July 2008 (UTC)

You must mean the inverse of Modulo operation?

When mod (a,b) = c,d where c=integer (a/b) d = remainder = a-(cb)

Then a = bc+a that's the nearest I can get to an inverse

If you only have c and d, then you get a range of values depending on what the divisor is.87.102.86.73 (talk) 23:33, 19 July 2008 (UTC)

Maybe Modular multiplicative inverse has what you want. PrimeHunter (talk) 00:07, 20 July 2008 (UTC)

Pretty much anything with "mod" in the name involves a loss of information, so it won't have a single-valued inverse. The best you can get is a family of inverses, like the one 87.102.86.73 mentions. We would need to know exactly what you mean by "mod" to help further, the term is used for various things. --Tango (talk) 00:21, 20 July 2008 (UTC)