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+13 votes
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The set \(\{1, 2, 4, 7, 8, 11, 13, 14\}\) is a group under multiplication modulo $15$. The inverses of $4$ and $7$ are respectively:

  1. $3$ and $13$
  2. $2$ and $11$
  3. $4$ and $13$
  4. $8$ and $14$
asked in Set Theory & Algebra by Boss (18.3k points)
edited by | 891 views

2 Answers

+17 votes
Best answer
Option C.

Identity element here is $1.$
$4 * 4 \mod 15 = 1$
$7 * 13 \mod 15 = 1.$
answered by Active (3.3k points)
selected by
+8

It is same as finding modular inverse, which is also last step in RSA.

You may likely to know actual procedure for even big numbers-

https://goo.gl/ZCza9r

​​​​​​​

–3 votes

The correct answer is,(c) 4 and 13

answered by Loyal (6.8k points)


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