Number Theory

Modular Arithmetic Operations

Modular Arithmetic - Multiplicative Inverses

Which of the following is correct?

A. 2 1 3 ( m o d 7 ) \ 2^{-1} \equiv 3 \pmod{7}
B. 3 1 4 ( m o d 7 ) \ 3^{-1} \equiv 4 \pmod{7}
C. 5 1 2 ( m o d 7 ) \ 5^{-1} \equiv 2 \pmod{7}
D. 6 1 6 ( m o d 7 ) \ 6^{-1} \equiv 6 \pmod{7}

What is 5 1 ( m o d 17 ) ? 5 ^ {-1} \pmod{17} ?

Hint:Remember that inverses multiply to 1.

What is

1 4 1 ( m o d 17 ) ? \large 14^{-1} \pmod{17} ?

What is 10 ! ( m o d 11 ) ? \large 10! \pmod{11}?

What is 2 1 ( m o d 39 ) ? 2 ^ {-1} \pmod{39} ?


Note: 2 1 ( m o d 39 ) 2^{-1} \pmod{39} is the integer k k such that 2 × k 1 ( m o d 39 ) . 2 \times k \equiv 1 \pmod{39}.

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