Skip to content
START WITH A QUESTION

What would you like to understand?

Find an answer. See the moment it becomes clear. Follow the idea further.

← Concept directory

Answers for “如何使用加模数法手动找到模逆元?”

5 keyword matches

Understanding your question. You can explore the search results below now.

Find a method

↗

To find the inverse of a modulo m by hand, start with 1 and repeatedly add the modulus m to generate numbers congruent to 1 modulo m. Stop when you reach a number that is a multiple of a.

Conditions: Used to find an inverse of a modulo m.; One looks among integers congruent to 1 modulo m for a multiple of a.

Know when to use it

↗

An integer a has an inverse modulo m if and only if the greatest common divisor of a and m is equal to 1, written as (a,m)=1(a,m)=1. If the greatest common divisor between a and m is greater than 1, then there is no inverse modulo m.

Conditions: a is an integer.; m is the modulus.; (a,m) denotes the greatest common divisor of a and m.

Meet the concept

↗

Two integers a and b are multiplicative inverses modulo m if their product is congruent to 1 modulo m. This is defined by the condition ab≡1(modm)ab \equiv 1 \pmod{m}.

Conditions: a and b are integers.; The congruence is taken modulo m.

Understand why

↗

5 has no inverse modulo 10 because the greatest common divisor of 5 and 10 is 5, which is not 1. According to the existence theorem, an integer has an inverse modulo m if and only if their gcd is 1.

Conditions: Modulus is 10.; Number whose inverse is requested: 5.

Meet the concept

↗

The inverse of 5 modulo 7 is 3. It is computed using the add-the-modulus method: start with 1, add 7 to get 8 (not a multiple of 5), add 7 again to get 15.

Conditions: Modulus is 7.; Target integer is 5.