Difference between revisions of "Modular arithmetic"

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=== Topics ===
 
=== Topics ===
 
* [[Fermat's Little Theorem]]
 
* [[Fermat's Little Theorem]]
* [[Euler's Theorem]]
+
* [[Euler's Totient Theorem]]
 
* [[Phi function]]
 
* [[Phi function]]
 
  
 
=== See also ===
 
=== See also ===

Revision as of 13:47, 19 June 2006

Modular arithmetic a special type of arithmetic that involves only integers. If two integers ${a},{b}$ leave the same remainder when they are divided by some positive integer ${m}$, we say that ${a}$ and $b$ are congruent modulo ${m}$ or $a\equiv b \pmod {m}$.


Introductory

Operations

Consider four integers ${a},{b},{c},{d}$ and a positive integer ${m}$ such that $a\equiv b\pmod {m}$ and $c\equiv d\pmod {m}$. In modular arithmetic, the following operations are allowed:

  • Addition: $a+c\equiv b+d\pmod {m}$.
  • Substraction: $a-c\equiv b-d\pmod {m}$.
  • Multiplication: $ac\equiv bd\pmod {m}$.
  • Division: $\frac{a}{e}\equiv \frac{b}{e}\pmod {\frac{m}{\gcd(m,e)}}$, where $e$ is a positive integer that divides ${a}$ and $b$.
  • Exponentiation: $a^e\equiv b^e\pmod {m}$ where $e$ is a positive integer.

Examples

  • ${7}\equiv {1} \pmod {2}$
  • $49^2\equiv 7^4\equiv (1)^4\equiv 1 \pmod {6}$
  • $7a\equiv 14\pmod {49}\implies a\equiv 2\pmod {7}$

Applications

Modular arithmetic is an extremely useful tool in mathematics competitions. It enables us to easily solve Linear diophantine equations, and it often helps with other Diophantine equations as well.


Intermediate

Topics

See also