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 “一个整数何时在模 m 下有逆元?”

3 keyword matches

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

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.