Friday 1 March 2019

elementary number theory - Euclid Algorithm to Find Muliplicative Inverse



Here I am trying to find the multiplicative inverse of 19 respect to 29.




$$19x \equiv 1 \pmod{29} $$



What I tried



\begin{align*}
29 &= 1(19) + 10\\\
19 &= 1(10) + 9\\\
10 &= 1(9) + 1.
\end{align*}




From backtracking, I came up with the



\begin{align*}
1 &= 2(29) - 3(19)\\\
\end{align*}



However, 3 is not a multiplicative inverse of the 29. Where am I making a mistake?



I looked many answers including this answer; however, couldn't figure out my mistake.



Answer



What you have found indeed is that $-3\equiv 26$ is the multiplicative inverse of $19$ $\mod 29$.


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