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Answers for “为什么 $15 \equiv 3 \pmod{12}$ 成立?”

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Understand why

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It is true because when 15 is divided by 12, the remainder is 3. This matches the definition of congruence modulo 12 used in the video.

Conditions: Use modulus 12.; Interpret the congruence via the remainder of division by 12.

Find a method

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To verify a≡b(modn)a \equiv b \pmod{n}, divide aa by the modulus nn using long division and check if the remainder is bb. If the remainder matches bb, the congruence is valid.

Conditions: The method is demonstrated for positive dividends and positive moduli.; The speaker calls it a colloquial explanation.

Meet the concept

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Congruence (≡\equiv) indicates that two numbers have the same remainder when divided by a modulus, whereas equality (==) means they are the exact same integer. The video uses congruence in cryptography instead of equality.

Conditions: Used in modular arithmetic contexts.; The modulus is explicitly shown in the examples (e.g., mod 12).