Math Path
MATH 01352 · Theory of Numbers

MATH 01352 · Congruences

Chinese Remainder Theorem idea

Definition

If m,n are coprime, the system x≡a (mod m), x≡b (mod n) has a unique solution mod mn. More generally for pairwise coprime moduli.

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Constructive proof: x = a n n⁻¹ + b m (m⁻¹) style combination (for two equations).

ℤ_{mn} ≅ ℤₘ × ℤₙ as rings when gcd(m,n)=1.

Used constantly in crypto and calendar/scheduling word problems.

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Attempt each problem first, then open the worked solution.

  1. 1.Solve x≡2 (mod 3), x≡3 (mod 5).