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Do you know a (simple) inverse modulo calculator somewhere on the Internet?

How to explain simply inverse modulo? (when the concept of modulo is already a bit known)

How to explain someone how to find a calculation resulting with a given modulo? For instance, finding a calculation with a modulo = 5.

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closed as off-topic by Chris Cunningham, Brendan W. Sullivan, JoeTaxpayer, kcrisman, Amy B May 20 '17 at 17:41

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    $\begingroup$ I'm not sure this is a good question for this site since it asks a question about how to calculate something instead of a question about mathematics education; you can find inverses modulo $n$ with the Euclidean Algorithm. See for example the "Extended Euclidean Algorithm" section at en.wikipedia.org/wiki/Modular_multiplicative_inverse $\endgroup$ – Chris Cunningham May 16 '17 at 16:50
  • $\begingroup$ And how to explain also... But do you think I should move my question? $\endgroup$ – Quidam May 17 '17 at 10:03
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For the first, there are a number of apps out there, though I will recommend that you go somewhat non-simple and use Sage. Are you looking for additive or multiplicative inverse? In either case, it is built-in.

a = Mod(3,7)
print -a
print a^-1

This gives 4 and 5, respectively.

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