What is the smallest positive integer n such that \(3n \equiv 1356 \pmod{22}? \)
What is the smallest positive integer n such that \(3n \equiv 1356 \pmod{22}\)
\(\begin{array}{|rcll|} \hline 3n &\equiv& 1356 \pmod{22} \\ 3n &\equiv& 1356-61*22 \pmod{22} \\ 3n &\equiv& 14 \pmod{22} \\ n &\equiv& \dfrac{14}{3} \pmod{22} \\ n &\equiv& 14*3^{-1} \pmod{22} \\ && \boxed{ 3^{-1} \pmod{22} = 3^{\phi(22)-1} \pmod{22} \quad | \quad \phi(22)=22*\left( 1-\dfrac{1}{2}\right)*\left( 1-\dfrac{1}{11}\right)=10 \\ =3^{10-1} \pmod{22} \\ = 3^9 \pmod{22} \\ = 19683 \pmod{22} \\ = 19683-894*22 \pmod{22} \\ = 15 \pmod{22} \\\mathbf{3^{-1} \pmod{22}=15 \pmod{22}} } \\ n &\equiv& 14*15 \pmod{22} \\ n &\equiv& 210 \pmod{22} \\ n &\equiv& 210-9*22 \pmod{22} \\ \mathbf{n} &\equiv& \mathbf{12 \pmod{22}} \\ \hline \end{array} \)
The smallest positive integer n is \(\mathbf{12}\)