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+11 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:

(a) 3 and 13

(b) 2 and 11

(c) 4 and 13

(d) 8 and 14
asked in Set Theory & Algebra by Veteran (17.9k points)
edited by | 691 views

2 Answers

+15 votes
Best answer
Option c.

Identity element here is 1.

4 * 4 mod 15 = 1

7 * 13 mod 15 = 1.
answered by Loyal (3.3k points)
selected by

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 Veteran (16.3k points)


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