Exercise · ZW-LAW-OF-QUADRATIC-RECIPROCITY-002 · ★☆☆ Basic
According to the law, when is \(\left(\frac{p}{q}\right)\left(\frac{q}{p}\right)=-1\)?
Choose one option.
Show answer
- B. When \(p\equiv q\equiv 3\pmod 4\)
Explanation
The product is \(-1\) only when both primes are congruent to 3 modulo 4. If both are congruent to 1 modulo 4, the product equals 1.
Review the concept: Law of quadratic reciprocity
The law of quadratic reciprocity relates the Legendre symbols \(\left(\frac{p}{q}\right)\) and \(\left(\frac{q}{p}\right)\) for distinct odd primes \(p\) and \(q\).
\[\left(\frac{p}{q}\right)\left(\frac{q}{p}\right)=(-1)^{\frac{(p-1)(q-1)}{4}}\]
More practice problems: law of quadratic reciprocity
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-001 State the law of quadratic reciprocity for distinct odd primes p and q.
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-003 Compute ((3)/(5))((5)/(3)).
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-004 What is the supplement formula for ((-1)/(p)) when p is an odd prime?
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-005 Compute ((2)/(7)).
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-006 Compute ((-1)/(7)).
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-007 Compute ((5)/(11)).
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-008 Does the congruence x^2≡ 3pmod11 have a solution?
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-009 By definition, when is ((a)/(p))=0?
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