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Solving linear congruences

  1. Apr 20, 2004 #1
    another little bit of help and this is NOT a homework assignment this is for an exam i need to understand it

    the qustion is find the decryption function for C = (7M + 9 ) mod 26

    how do i fin the decryption function using the inverse?

    that is 15 in this case
  2. jcsd
  3. Apr 21, 2004 #2

    matt grime

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    Homework Helper

    the same way you do it for any other equation:
    you've just got to find what the multiplicative inverse of 7 is in U(26)
    I don't see where 15 comes from.
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